Articles | Volume 21, issue 4
https://doi.org/10.5194/os-21-1349-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-21-1349-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
14 Jul 2025
Research article |
| 14 Jul 2025
| 14 Jul 2025
On mode water formation and erosion in the Arabian Sea: forcing mechanisms, regionality, and seasonality
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
Sebastiaan Swart
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
Department of Oceanography, University of Cape Town, Rondebosch, South Africa
Puthenveettil Narayana Vinayachandran
Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru, India
Bastien Y. Queste
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
Related authors
Estel Font, Esther Portela, Sebastiaan Swart, Mauro Pinto-Juica, and Bastien Y. Queste
EGUsphere, https://doi.org/10.5194/egusphere-2025-3782, https://doi.org/10.5194/egusphere-2025-3782, 2025
This preprint is open for discussion and under review for Ocean Science (OS).
Short summary
Short summary
In the Sea of Oman, mode waters form at the surface in winter and are trapped beneath a warmer surface layer in spring, linking the surface ocean and the oxygen minimum zone. Using data from ocean gliders, our study examines how this layer evolves. Changes occur along layers of equal density, with brief episodes of vertical mixing, enhanced by eddies. Glider data reveal more variability than monthly means, showing the need for sustained glider observations to understand future ecosystem impacts.
Estel Font, Esther Portela, Sebastiaan Swart, Mauro Pinto-Juica, and Bastien Y. Queste
EGUsphere, https://doi.org/10.5194/egusphere-2025-3782, https://doi.org/10.5194/egusphere-2025-3782, 2025
This preprint is open for discussion and under review for Ocean Science (OS).
Short summary
Short summary
In the Sea of Oman, mode waters form at the surface in winter and are trapped beneath a warmer surface layer in spring, linking the surface ocean and the oxygen minimum zone. Using data from ocean gliders, our study examines how this layer evolves. Changes occur along layers of equal density, with brief episodes of vertical mixing, enhanced by eddies. Glider data reveal more variability than monthly means, showing the need for sustained glider observations to understand future ecosystem impacts.
Peter M. F. Sheehan, Benjamin G. M. Webber, Alejandra Sanchez-Franks, and Bastien Y. Queste
Ocean Sci., 21, 1575–1588, https://doi.org/10.5194/os-21-1575-2025, https://doi.org/10.5194/os-21-1575-2025, 2025
Short summary
Short summary
Using measurements and computer models, we identify a large flux of oxygen within the Southwest Monsoon Current, which flows north into the Bay of Bengal between June and September each year. Oxygen levels in the bay are very low, but they are not quite low enough for key nutrient cycles to be as dramatically altered as in other low-oxygen regions. We suggest that the flux which we identify contributes to keeping oxygen levels in the bay above the threshold below which dramatic changes would occur.
Renske Koets, Sebastiaan Swart, Kathleen Donohue, and Marcel du Plessis
EGUsphere, https://doi.org/10.5194/egusphere-2025-3112, https://doi.org/10.5194/egusphere-2025-3112, 2025
This preprint is open for discussion and under review for Ocean Science (OS).
Short summary
Short summary
The Cape Basin is a dynamic region where warm, salty Indian Ocean waters meet cooler Atlantic waters. Mixing between these waters drives ventilation, the transport of surface waters to deeper layers in the ocean. Using high-resolution observations from an autonomous Seaglider combined with satellite altimetry we provide new evidence on how small-scale ocean dynamics contribute to ventilation in the Cape Basin, with broader implications on ocean circulation.
Daisy Drew Pickup, Dorothee C. E. Bakker, Karen J. Heywood, Francis Glassup, Emily Hammermeister, Sharon E. Stammerjohn, Gareth A. Lee, Socratis Loucaides, Bastien Y. Queste, Benjamin G. M. Webber, and Patricia L. Yager
EGUsphere, https://doi.org/10.5194/egusphere-2025-2441, https://doi.org/10.5194/egusphere-2025-2441, 2025
Short summary
Short summary
Autonomous platforms in the Amundsen Sea have allowed for detection of isolated water masses that are colder, saltier and denser than overlying water. They are also associated with a higher dissolved inorganic carbon concentration and lower pH. The water masses, referred to as lenses, could have implications for the transfer of heat and storage of carbon in the region. We hypothesise that they form in surrounding areas that experience intense cooling and sea ice formation in autumn/winter.
Kirtana Naëck, Jacqueline Boutin, Sebastiaan Swart, Marcel du Plessis, Liliane Merlivat, Laurence Beaumont, Antonio Lourenco, Francesco d'Ovidio, Louise Rousselet, Brian Ward, and Jean-Baptiste Sallée
Biogeosciences, 22, 1947–1968, https://doi.org/10.5194/bg-22-1947-2025, https://doi.org/10.5194/bg-22-1947-2025, 2025
Short summary
Short summary
In summer 2022, a CARbon Interface OCean Atmosphere (CARIOCA) drifting buoy observed an anomalously strong ocean carbon sink in the subpolar Southern Ocean associated with large plumes of chlorophyll a. Lagrangian backward trajectories indicate that these waters originated from the sea ice edge in spring 2021. Our study highlights the northward migration of the CO2 sink associated with early sea ice retreat.
Blandine Jacob, Bastien Y. Queste, and Marcel D. du Plessis
Ocean Sci., 21, 359–379, https://doi.org/10.5194/os-21-359-2025, https://doi.org/10.5194/os-21-359-2025, 2025
Short summary
Short summary
Few observations exist in the Amundsen Sea. Consequently, studies rely on reanalysis (e.g., ERA5) to investigate how the atmosphere affects ocean variability (e.g., sea-ice formation and melt). We use data collected along ice shelves to show that cold, dry air blowing from Antarctica triggers large ocean heat loss, which is underestimated by ERA5. We then use an ocean model to show that this bias has an important impact on the ocean, with implications for sea-ice forecasts.
Ria Oelerich, Karen J. Heywood, Gillian M. Damerell, Marcel du Plessis, Louise C. Biddle, and Sebastiaan Swart
Ocean Sci., 19, 1465–1482, https://doi.org/10.5194/os-19-1465-2023, https://doi.org/10.5194/os-19-1465-2023, 2023
Short summary
Short summary
At the southern boundary of the Antarctic Circumpolar Current, relatively warm waters encounter the colder waters surrounding Antarctica. Observations from underwater vehicles and altimetry show that medium-sized cold-core eddies influence the southern boundary's barrier properties by strengthening the slopes of constant density lines across it and amplifying its associated jet. As a result, the ability of exchanging properties, such as heat, across the southern boundary is reduced.
Elise S. Droste, Mario Hoppema, Melchor González-Dávila, Juana Magdalena Santana-Casiano, Bastien Y. Queste, Giorgio Dall'Olmo, Hugh J. Venables, Gerd Rohardt, Sharyn Ossebaar, Daniel Schuller, Sunke Trace-Kleeberg, and Dorothee C. E. Bakker
Ocean Sci., 18, 1293–1320, https://doi.org/10.5194/os-18-1293-2022, https://doi.org/10.5194/os-18-1293-2022, 2022
Short summary
Short summary
Tides affect the marine carbonate chemistry of a coastal polynya neighbouring the Ekström Ice Shelf by movement of seawater with different physical and biogeochemical properties. The result is that the coastal polynya in the summer can switch between being a sink or a source of CO2 multiple times a day. We encourage consideration of tides when collecting in polar coastal regions to account for tide-driven variability and to avoid overestimations or underestimations of air–sea CO2 exchange.
Benjamin R. Loveday, Timothy Smyth, Anıl Akpinar, Tom Hull, Mark E. Inall, Jan Kaiser, Bastien Y. Queste, Matt Tobermann, Charlotte A. J. Williams, and Matthew R. Palmer
Earth Syst. Sci. Data, 14, 3997–4016, https://doi.org/10.5194/essd-14-3997-2022, https://doi.org/10.5194/essd-14-3997-2022, 2022
Short summary
Short summary
Using a new approach to combine autonomous underwater glider data and satellite Earth observations, we have generated a 19-month time series of North Sea net primary productivity – the rate at which phytoplankton absorbs carbon dioxide minus that lost through respiration. This time series, which spans 13 gliders, allows for new investigations into small-scale, high-frequency variability in the biogeochemical processes that underpin the carbon cycle and coastal marine ecosystems in shelf seas.
Yixi Zheng, David P. Stevens, Karen J. Heywood, Benjamin G. M. Webber, and Bastien Y. Queste
The Cryosphere, 16, 3005–3019, https://doi.org/10.5194/tc-16-3005-2022, https://doi.org/10.5194/tc-16-3005-2022, 2022
Short summary
Short summary
New observations reveal the Thwaites gyre in a habitually ice-covered region in the Amundsen Sea for the first time. This gyre rotates anticlockwise, despite the wind here favouring clockwise gyres like the Pine Island Bay gyre – the only other ocean gyre reported in the Amundsen Sea. We use an ocean model to suggest that sea ice alters the wind stress felt by the ocean and hence determines the gyre direction and strength. These processes may also be applied to other gyres in polar oceans.
Puthenveettil Narayana Menon Vinayachandran, Yukio Masumoto, Michael J. Roberts, Jenny A. Huggett, Issufo Halo, Abhisek Chatterjee, Prakash Amol, Garuda V. M. Gupta, Arvind Singh, Arnab Mukherjee, Satya Prakash, Lynnath E. Beckley, Eric Jorden Raes, and Raleigh Hood
Biogeosciences, 18, 5967–6029, https://doi.org/10.5194/bg-18-5967-2021, https://doi.org/10.5194/bg-18-5967-2021, 2021
Short summary
Short summary
Upwelling in the coastal ocean triggers biological productivity and thus enhances fisheries. Therefore, understanding the phenomenon of upwelling and the underlying mechanisms is important. In this paper, the present understanding of the upwelling along the coastline of the Indian Ocean from the coast of Africa all the way up to the coast of Australia is reviewed. The review provides a synthesis of the physical processes associated with upwelling and its impact on the marine ecosystem.
Jack Giddings, Karen J. Heywood, Adrian J. Matthews, Manoj M. Joshi, Benjamin G. M. Webber, Alejandra Sanchez-Franks, Brian A. King, and Puthenveettil N. Vinayachandran
Ocean Sci., 17, 871–890, https://doi.org/10.5194/os-17-871-2021, https://doi.org/10.5194/os-17-871-2021, 2021
Short summary
Short summary
Little is known about the impact of chlorophyll on SST in the Bay of Bengal (BoB). Solar irradiance measured by an ocean glider and three Argo floats is used to determine the effect of chlorophyll on BoB SST during the 2016 summer monsoon. The Southwest Monsoon Current has high chlorophyll concentrations (∼0.5 mg m−3) and shallow solar penetration depths (∼14 m). Ocean mixed layer model simulations show that SST increases by 0.35°C per month, with the potential to influence monsoon rainfall.
Venugopal Thushara, Puthenveettil Narayana Menon Vinayachandran, Adrian J. Matthews, Benjamin G. M. Webber, and Bastien Y. Queste
Biogeosciences, 16, 1447–1468, https://doi.org/10.5194/bg-16-1447-2019, https://doi.org/10.5194/bg-16-1447-2019, 2019
Short summary
Short summary
Chlorophyll distribution in the ocean remains to be explored in detail, despite its climatic significance. Here, we document the vertical structure of chlorophyll in the Bay of Bengal using observations and a model. The shape of chlorophyll profiles, characterized by prominent deep chlorophyll maxima, varies in dynamically different regions, controlled by the monsoonal forcings. The present study provides new insights into the vertical distribution of chlorophyll, rarely observed by satellites.
Reiner Onken, Heinz-Volker Fiekas, Laurent Beguery, Ines Borrione, Andreas Funk, Michael Hemming, Jaime Hernandez-Lasheras, Karen J. Heywood, Jan Kaiser, Michaela Knoll, Baptiste Mourre, Paolo Oddo, Pierre-Marie Poulain, Bastien Y. Queste, Aniello Russo, Kiminori Shitashima, Martin Siderius, and Elizabeth Thorp Küsel
Ocean Sci., 14, 321–335, https://doi.org/10.5194/os-14-321-2018, https://doi.org/10.5194/os-14-321-2018, 2018
Short summary
Short summary
In June 2014, high-resolution oceanographic data were collected in the
western Mediterranean Sea by two research vessels, 11 gliders, moored
instruments, drifters, and one profiling float. The objective
of this article is to provide an overview of the data set which
is utilised by various ongoing studies, focusing on (i) water masses and circulation, (ii) operational forecasting, (iii) data assimilation, (iv) variability of the ocean, and (v) new payloads
for gliders.
Peter M. F. Sheehan, Barbara Berx, Alejandro Gallego, Rob A. Hall, Karen J. Heywood, Sarah L. Hughes, and Bastien Y. Queste
Ocean Sci., 14, 225–236, https://doi.org/10.5194/os-14-225-2018, https://doi.org/10.5194/os-14-225-2018, 2018
Short summary
Short summary
We calculate tidal velocities using observations of ocean currents collected by an underwater glider. We use these velocities to investigate the location of sharp boundaries between water masses in shallow seas. Narrow currents along these boundaries are important transport pathways around shallow seas for pollutants and organisms. Tides are an important control on boundary location in summer, but seawater salt concentration can also influence boundary location, especially in winter.
Michaela Knoll, Ines Borrione, Heinz-Volker Fiekas, Andreas Funk, Michael P. Hemming, Jan Kaiser, Reiner Onken, Bastien Queste, and Aniello Russo
Ocean Sci., 13, 889–904, https://doi.org/10.5194/os-13-889-2017, https://doi.org/10.5194/os-13-889-2017, 2017
Short summary
Short summary
The hydrography and circulation west of Sardinia, observed in June 2014 during REP14-MED by means of various measuring platforms, are presented and compared with previous knowledge. So far, the circulation of this area is not well-known and the hydrography is subject to long-term changes. The different water masses are characterized and temporal changes are emphasized. The observed eddies are specified and geostrophic transports in the upper ocean are presented.
Bastien Y. Queste, Liam Fernand, Timothy D. Jickells, Karen J. Heywood, and Andrew J. Hind
Biogeosciences, 13, 1209–1222, https://doi.org/10.5194/bg-13-1209-2016, https://doi.org/10.5194/bg-13-1209-2016, 2016
Short summary
Short summary
In stratified shelf seas, physical and biological conditions can lead to seasonal oxygen depletion when consumption exceeds supply. An ocean glider obtained a high-resolution 3-day data set of biochemical and physical properties in the central North Sea. The data revealed very high oxygen consumption rates, far exceeding previously reported rates. A consumption–supply oxygen budget indicates a localized or short-lived resuspension event causing rapid remineralization of benthic organic matter.
Related subject area
Approach: In situ Observations | Properties and processes: Overturning circulation, gyres and water masses
Seasonality of meridional overturning in the subpolar North Atlantic: density flux as a metric for understanding the Atlantic meridional overturning circulation
Hydrographic section along 55° E in the Indian and Southern oceans
Circulation of Baffin Bay and Hudson Bay waters on the Labrador shelf and into the subpolar North Atlantic
Mechanisms of the Overturning Circulation in the Northern Red Sea, more than Convective Mixing
Continued warming of deep waters in the Fram Strait
Observed change and the extent of coherence in the Gulf Stream system
Anomalous North Pacific subtropical mode water volume and density decrease in a recent stable Kuroshio Extension period from Argo observations
New insights into the eastern subpolar North Atlantic meridional overturning circulation from OVIDE
The Southern Ocean deep mixing band emerges from a competition between winter buoyancy loss and upper stratification strength
Comparing observed and modelled components of the Atlantic Meridional Overturning Circulation at 26° N
Water properties and bottom water patterns in hadal trench environments
Long-term eddy modulation affects the meridional asymmetry of the halocline in the Beaufort Gyre
Technical note: Determining Arctic Ocean halocline and cold halostad depths based on vertical stability
The Iceland–Faroe warm-water flow towards the Arctic estimated from satellite altimetry and in situ observations
Alan D. Fox, Neil J. Fraser, and Stuart A. Cunningham
Ocean Sci., 21, 1735–1760, https://doi.org/10.5194/os-21-1735-2025, https://doi.org/10.5194/os-21-1735-2025, 2025
Short summary
Short summary
Understanding the seasonality of the overturning circulation is important for mitigating the impacts of Atlantic meridional overturning circulation (AMOC) changes on European weather and climate. We examine the seasonal cycle in various common measures of overturning and find each to be dominated by different processes, not necessarily reflective of the processes driving overturning. We advocate for the use of a density flux measure as a valuable addition to understanding AMOC.
Katsuro Katsumata, Shigeru Aoki, Kay I. Ohshima, and Michiyo Yamamoto-Kawai
Ocean Sci., 21, 419–436, https://doi.org/10.5194/os-21-419-2025, https://doi.org/10.5194/os-21-419-2025, 2025
Short summary
Short summary
Ship-based observations provide data of seawater properties like temperature, salinity, nutrients, and various gases, but some important world oceans have still not been covered. A voyage in 2019/20 in the southwest Indian Ocean along approximately 55° E from 30° S to Antarctica attempted to fill one such data-sparse region. The measured cross section of the Antarctic Circumpolar Current and accompanying eddies demonstrates various oceanic behaviours including fronts and eddy mixing.
Elodie Duyck, Nicholas P. Foukal, and Eleanor Frajka-Williams
Ocean Sci., 21, 241–260, https://doi.org/10.5194/os-21-241-2025, https://doi.org/10.5194/os-21-241-2025, 2025
Short summary
Short summary
This study uses drifters – instruments that follow surface ocean currents – to investigate the pathways of Arctic origin waters that enter the North Atlantic west of Greenland. It shows that these waters remain close to the coast as they flow over the Labrador shelf and only spread into the open ocean south of the Labrador Sea. These results contribute to better understanding how the North Atlantic will be affected by additional freshwater from Greenland and the Arctic in the coming decades.
Lina Eyouni, Zoi Kokkini, Nikolaos D. Zarokanellos, and Burton H. Jones
EGUsphere, https://doi.org/10.5194/egusphere-2024-3319, https://doi.org/10.5194/egusphere-2024-3319, 2024
Short summary
Short summary
This study examines how multiple processes in the Northern Red Sea form the Red Sea Outflow Water and affect biogeochemical fluxes. Using glider data, wind and air-sea flux reanalysis, and satellite observations, it highlights seasonal evolution. Eddy-driven upwelling exposes cool water to heat loss and evaporation, fueling primary productivity. Circulation patterns block inflows, extend cooling, and subduct water into the ocean interior, influencing regional dynamics.
Salar Karam, Céline Heuzé, Mario Hoppmann, and Laura de Steur
Ocean Sci., 20, 917–930, https://doi.org/10.5194/os-20-917-2024, https://doi.org/10.5194/os-20-917-2024, 2024
Short summary
Short summary
A long-term mooring array in the Fram Strait allows for an evaluation of decadal trends in temperature in this major oceanic gateway into the Arctic. Since the 1980s, the deep waters of the Greenland Sea and the Eurasian Basin of the Arctic have warmed rapidly at a rate of 0.11°C and 0.05°C per decade, respectively, at a depth of 2500 m. We show that the temperatures of the two basins converged around 2017 and that the deep waters of the Greenland Sea are now a heat source for the Arctic Ocean.
Helene Asbjørnsen, Tor Eldevik, Johanne Skrefsrud, Helen L. Johnson, and Alejandra Sanchez-Franks
Ocean Sci., 20, 799–816, https://doi.org/10.5194/os-20-799-2024, https://doi.org/10.5194/os-20-799-2024, 2024
Short summary
Short summary
The Gulf Stream system is essential for northward ocean heat transport. Here, we use observations along the path of the extended Gulf Stream system and an observationally constrained ocean model to investigate variability in the Gulf Stream system since the 1990s. We find regional differences in the variability between the subtropical, subpolar, and Nordic Seas regions, which warrants caution in using observational records at a single latitude to infer large-scale circulation change.
Jing Sheng, Cong Liu, Yanzhen Gu, Peiliang Li, Fangguo Zhai, and Ning Zhou
Ocean Sci., 20, 817–834, https://doi.org/10.5194/os-20-817-2024, https://doi.org/10.5194/os-20-817-2024, 2024
Short summary
Short summary
The homogeneous water column, named mode water, retains atmosphere conditions and biogeochemical elements from the deep winter mixed layer and became weaker and warmer in the North Pacific subtropical ocean in 2018–2021 even though the Kuroshio Extension was stable. Locally anomalous east wind transporting warm water to the north and enhanced near-surface stratification hinder the deepening of the winter mixed layer. This study has broad implications for climate change and biogeochemical cycles.
Herlé Mercier, Damien Desbruyères, Pascale Lherminier, Antón Velo, Lidia Carracedo, Marcos Fontela, and Fiz F. Pérez
Ocean Sci., 20, 779–797, https://doi.org/10.5194/os-20-779-2024, https://doi.org/10.5194/os-20-779-2024, 2024
Short summary
Short summary
We study the Atlantic Meridional Overturning Circulation (AMOC) measured between Greenland and Portugal between 1993–2021. We identify changes in AMOC limb volume and velocity as two major drivers of AMOC variability at subpolar latitudes. Volume variations dominate on the seasonal timescale, while velocity variations are more important on the decadal timescale. This decomposition proves useful for understanding the origin of the differences between AMOC time series from different analyses.
Romain Caneill, Fabien Roquet, and Jonas Nycander
Ocean Sci., 20, 601–619, https://doi.org/10.5194/os-20-601-2024, https://doi.org/10.5194/os-20-601-2024, 2024
Short summary
Short summary
In winter, heat loss increases density at the surface of the Southern Ocean. This increase in density creates a mixed layer deeper than 250 m only in a narrow deep mixing band (DMB) located around 50° S. North of the DMB, the stratification is too strong to be eroded, so mixed layers are shallower. The density of cold water is almost not impacted by temperature changes. Thus, heat loss does not significantly increase the density south of the DMB, so no deep mixed layers are produced.
Harry Bryden, Jordi Beunk, Sybren Drijfhout, Wilco Hazeleger, and Jennifer Mecking
Ocean Sci., 20, 589–599, https://doi.org/10.5194/os-20-589-2024, https://doi.org/10.5194/os-20-589-2024, 2024
Short summary
Short summary
There is widespread interest in whether the Gulf Stream will decline under global warming. We analyse 19 coupled climate model projections of the AMOC over the 21st century. The model consensus is that the AMOC will decline by about 40 % due to reductions in northward Gulf Stream transport and southward deep western boundary current transport. Whilst the wind-driven Gulf Stream decreases by 4 Sv, most of the decrease in the Gulf Stream is due to a reduction of 7 Sv in its thermohaline component.
Jessica Kolbusz, Jan Zika, Charitha Pattiaratchi, and Alan Jamieson
Ocean Sci., 20, 123–140, https://doi.org/10.5194/os-20-123-2024, https://doi.org/10.5194/os-20-123-2024, 2024
Short summary
Short summary
We collected observations of the ocean environment at depths over 6000 m in the Southern Ocean, Indian Ocean, and western Pacific using sensor-equipped landers. We found that trench locations impact the water characteristics over these depths. Moving northward, they generally warmed but differed due to their position along bottom water circulation paths. These insights stress the importance of further research in understanding the environment of these deep regions and their importance.
Jinling Lu, Ling Du, and Shuhao Tao
Ocean Sci., 19, 1773–1789, https://doi.org/10.5194/os-19-1773-2023, https://doi.org/10.5194/os-19-1773-2023, 2023
Short summary
Short summary
With the recent developments in observations and reanalysis data in the Beaufort Gyre, we investigate an improved understanding of eddy activity and asymmetrical halocline variability in the upper ocean. The halocline structures on the southern and northern sides of the central gyre have tended to be identical since 2014. The results suggest that enhanced eddy modulation through eddy fluxes influences oceanic stratification, resulting in reduced meridional asymmetry of the halocline.
Enrico P. Metzner and Marc Salzmann
Ocean Sci., 19, 1453–1464, https://doi.org/10.5194/os-19-1453-2023, https://doi.org/10.5194/os-19-1453-2023, 2023
Short summary
Short summary
The Arctic Ocean cold halocline separates the cold surface mixed layer from the underlying warm Atlantic Water, and thus provides a precondition for sea ice formation. Here, we introduce a new method for detecting the halocline base and compare it to two existing methods. We show that the largest differences between the methods are found in the regions that are most prone to a halocline retreat in a warming climate, and we discuss the advantages and disadvantages of the three methods.
Bogi Hansen, Karin M. H. Larsen, Hjálmar Hátún, Steffen M. Olsen, Andrea M. U. Gierisch, Svein Østerhus, and Sólveig R. Ólafsdóttir
Ocean Sci., 19, 1225–1252, https://doi.org/10.5194/os-19-1225-2023, https://doi.org/10.5194/os-19-1225-2023, 2023
Short summary
Short summary
Based on in situ observations combined with sea level anomaly (SLA) data from satellite altimetry, volume as well as heat (relative to 0 °C) transport of the Iceland–Faroe warm-water inflow towards the Arctic (IF inflow) increased from 1993 to 2021. The reprocessed SLA data released in December 2021 represent observed variations accurately. The IF inflow crosses the Iceland–Faroe Ridge in two branches, with retroflection in between. The associated coupling to overflow reduces predictability.
Cited articles
Acharya, S. S. and Panigrahi, M. K.: Eastward shift and maintenance of Arabian Sea oxygen minimum zone: Understanding the paradox, Deep-Sea Res. Pt. I, 115, 240–252, https://doi.org/10.1016/j.dsr.2016.07.004, 2016.
Albert, J., Gulakaram, V. S., Vissa, N. K., Bhaskaran, P. K., and Dash, M. K.: Recent warming trends in the Arabian Sea: Causative factors and physical mechanisms, Climate, 11, 35, https://doi.org/10.3390/CLI11020035, 2023.
Argo: Argo float data and metadata from Global Data Assembly Centre (Argo GDAC), SEANOE [data set], https://doi.org/10.17882/42182, 2023.
Babu, K. N., Sharma, R., Agarwal, N., Agarwal, V. K., Weller, R. A., and Babu, C.: Study of the mixed layer depth variations within the north Indian Ocean using a 1-D model, J. Geophys. Res.-Oceans, 109, 8016, https://doi.org/10.1029/2003JC002024, 2004.
Beal, L. M., Hormann, V., Lumpkin, R., and Foltz, G. R.: The response of the surface circulation of the Arabian Sea to monsoonal forcing, J. Phys. Oceanogr., 43, 2008–2022, https://doi.org/10.1175/JPO-D-13-033.1, 2013.
Behara, A. and Vinayachandran, P. N.: An OGCM study of the impact of rain and river water forcing on the Bay of Bengal, J. Geophys. Res.-Oceans, 121, 2425–2446, https://doi.org/10.1002/2015JC011325, 2016.
Burchard, H., Bolding, K., and Villarreal, M. R.: GOTM, a General Ocean Turbulence Model: Theory, implementation and test cases, Tech. Rep. EUR 18745, p. 103, European Commission, https://op.europa.eu/en/publication-detail/-/publication/5b512e12-367d-11ea-ba6e-01aa75ed71a1 (last access: 10 March 2025), 1999.
Bushinsky, S. M. and Cerovečki, I.: Subantarctic Mode Water biogeochemical formation properties and interannual variability, AGU Adv., 4, e2022AV000722, https://doi.org/10.1029/2022AV000722, 2023.
Bopp, L., Resplandy, L., Orr, J. C., Doney, S. C., Dunne, J. P., Gehlen, M., Halloran, P., Heinze, C., Ilyina, T., Séférian, R., Tjiputra, J., and Vichi, M.: Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models, Biogeosciences, 10, 6225–6245, https://doi.org/10.5194/bg-10-6225-2013, 2013.
Chaichitehrani, N. and Allahdadi, M. N.: Overview of wind climatology for the Gulf of Oman and the northern Arabian Sea, Am. J. Fluid Dyn., 8, 1–9, http://article.sapub.org/10.5923.j.ajfd.20180801.01.html (last access: 10 March 2025), 2018
Chatterjee, A., Shankar, D., Shenoi, S. S. C., Reddy, G. V., Michael, G. S., Ravichandran, M., Gopalkrishna, V. V., Rao, E. P. R., Bhaskar, T. V. S. U., and Sanjeevan, V. N.: A new atlas of temperature and salinity for the North Indian Ocean, J. Earth Syst. Sci., 121, 559–593, https://doi.org/10.1007/s12040-012-0191-9, 2012.
Cheng, Y., Wang, L., Chen, X., Zhou, T., and Turner, A.: A shorter duration of the Indian summer monsoon in constrained projections, Geophys. Res. Lett., 52, e2024GL112848, https://doi.org/10.1029/2024GL112848, 2025.
Chowdary, J. S., Gnanaseelan, C., Thompson, B., and Salvekar, P. S.: Water mass properties and transports in the Arabian Sea from Argo observations, Atmos. Ocean Sci., 10, 235–260, https://doi.org/10.1080/17417530600752825, 2005.
Dall'Olmo, G., Dingle, J., Polimene, L., Brewin, R. J. W., and Claustre, H.: Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump, Nat. Geosci., 9, 820–823, https://doi.org/10.1038/ngeo2818, 2016.
Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S. B., Hersbach, H., Hólm, E. V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrette, J.-J., Park, B.-K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J.-N., and Vitart, F.: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system, Q. J. Roy. Meteor. Soc., 137, 553–597, https://doi.org/10.1002/qj.828, 2011.
de Marez, C., L'Hégaret, P., Morvan, M., and Carton, X.: On the 3D structure of eddies in the Arabian Sea, Deep-Sea Res. Pt. I, 150, 103057, https://doi.org/10.1016/j.dsr.2019.06.003, 2019.
Ditkovsky, S., Resplandy, L., and Busecke, J.: Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming, Biogeosciences, 20, 4711–4736, https://doi.org/10.5194/bg-20-4711-2023, 2023.
Dunne, J. P., Gnanadesikan, A., Sarmiento, J. L., and Slater, R. D.: Technical description of the prototype version (v0) of tracers of phytoplankton with allometric zooplankton (TOPAZ) ocean biogeochemical model as used in the Princeton IFMIP model, Technical report, https://bg.copernicus.org/articles/7/3593/2010/bg-7-3593-2010-supplement.pdf (last access: 10 March 2025), 2010.
Echols, R. and Riser, S. C.: The impact of barrier layers on Arabian Sea surface temperature variability, Geophys. Res. Lett., 47, e2019GL085290, https://doi.org/10.1029/2019GL085290, 2020.
Feucher, C., Maze, G., and Mercier, H.: Subtropical Mode Water and permanent pycnocline properties in the world ocean, J. Geophys. Res.-Oceans, 124, 1139–1154, https://doi.org/10.1029/2018JC014526, 2019.
Font, E.: EstelFont/Mode_Water_Arabian_Sea: v1.0.0, Zenodo [code], https://doi.org/10.5281/zenodo.15834677, 2025.
Font, E. and Vinaychandran, P. N.: MOM4p1-TOPAZ data used in the manuscript entitled “On Mode Water formation and erosion in the Arabian Sea: Forcing mechanisms, regionality, and seasonality” (v1.0), Zenodo [data set], https://doi.org/10.5281/zenodo.14770956, 2025.
Font, E., Queste, B. Y., and Swart, S.: Seasonal to intraseasonal variability of the upper ocean mixed layer in the Gulf of Oman, J. Geophys. Res.-Oceans, 127, e2021JC018045, https://doi.org/10.1029/2021JC018045, 2022.
Gaillard, F., Autret, E., Thierry, V., Galaup, P., Coatanoan, C., and Loubrieu, T.: Quality control of large Argo datasets, J. Atmos. Ocean. Tech., 26, 337–351, https://doi.org/10.1175/2008JTECHO552.1, 2009.
Gao, Z., Long, S. M., Shi, J. R., Cheng, L., Li, G., and Ying, J.: Indian Ocean mixed layer depth changes under global warming, Front. Clim., 5, 1112713, https://doi.org/10.3389/fclim.2023.1112713, 2023.
GEBCO Compilation Group: GEBCO 2023 Grid, NERC EDS British Oceanographic Data Centre NOC [data set], https://doi.org/10.5285/f98b053b-0cbc-6c23-e053-6c86abc0af7b, 2023.
Griffies, S. M. and Hallberg, R. W.: Biharmonic Friction with a Smagorinsky-Like Viscosity for Use in Large-Scale Eddy-Permitting Ocean Models, Mon. Weather Rev., 128, 2935–2946, https://doi.org/10.1175/1520-0493(2000)128<2935:BFWASL>2.0.CO;2, 2000.
Griffies, S. M., Harrison, M. J., Pacanowski, R. C., and Rosati, A.: A technical guide to MOM4, GFDL Ocean Group Technical Report No. 5, NOAA/Geophysical Fluid Dynamics Laboratory, Version prepared on 23 August 2004, https://www.gfdl.noaa.gov (last access: 10 March 2025), 2003.
Han, W. and McCreary, J. P.: Modeling salinity distributions in the Indian Ocean, J. Geophys. Res.-Oceans, 106, 859–877, https://doi.org/10.1029/2000JC000316, 2001.
Hanawa, K. and Talley, L. D.: Chapter 5.4 Mode waters, Int. Geophys., 77, 373–386, https://doi.org/10.1016/S0074-6142(01)80129-7, 2001.
Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., Muñoz-Sabater, J., Nicolas, J., Peubey, C., Radu, R., Schepers, D., Simmons, A., Soci, C., Abdalla, S., Abellan, X., Balsamo, G., Bechtold, P., Biavati, G., Bidlot, J., Bonavita, M., De Chiara, G., Dahlgren, P., Dee, D., Diamantakis, M., Dragani, R., Flemming, J., Forbes, R., Fuentes, M., Geer, A., Haimberger, L., Healy, S., Hogan, R. J., Hólm, E., Janisková, M., Keeley, S., Laloyaux, P., Lopez, P., Lupu, C., Radnoti, G., de Rosnay, P., Rozum, I., Vamborg, F., Villaume, S., and Thépaut, J. N.: The ERA5 global reanalysis, Q. J. Roy. Meteor. Soc., 146, 1999–2049, https://doi.org/10.1002/qj.3803, 2020.
Hooker, S. B. and Esaias, W. E.: An overview of the SeaWiFS Project, Eos Trans. Am. Geophys. Union, 74, 241–246, https://doi.org/10.1029/93EO00945, 1993.
Kalvelage, T., Lavik, G., Jensen, M. M., Revsbech, N. P., Löscher, C., Schunck, H., Desai, D. K., Hauss, H., Kiko, R., Holtappels, M., LaRoche, J., Schmitz, R. A., Graco, M. I., and Kuypers, M. M. M.: Aerobic microbial respiration in oceanic oxygen minimum zones, PLoS ONE, 10, e0133526, https://doi.org/10.1371/journal.pone.0133526, 2015.
Karleskind, P., Lévy, M., and Mémery, L.: Modifications of mode water properties by sub-mesoscales in a bio-physical model of the Northeast Atlantic, Ocean Model., 39, 47–60, https://doi.org/10.1016/j.ocemod.2010.12.003, 2011.
Kumar, S. P. and Prasad, T. G.: Formation and spreading of Arabian Sea high-salinity water mass, J. Geophys. Res.-Oceans, 104, 1455–1464, https://doi.org/10.1029/1998JC900022, 1999.
Kurian, J. and Vinayachandran, P. N.: Formation mechanisms of temperature inversions in the southeastern Arabian Sea, Geophys. Res. Lett., 33, L17611, https://doi.org/10.1029/2006GL027280, 2006.
Kurian, J. and Vinayachandran, P. N.: Mechanisms of formation of the Arabian Sea mini warm pool in a high-resolution ocean general circulation model, J. Geophys. Res.-Oceans, 112, C05009, https://doi.org/10.1029/2006JC003631, 2007.
Kwiatkowski, L., Torres, O., Bopp, L., Aumont, O., Chamberlain, M., Christian, J. R., Dunne, J. P., Gehlen, M., Ilyina, T., John, J. G., Lenton, A., Li, H., Lovenduski, N. S., Orr, J. C., Palmieri, J., Santana-Falcón, Y., Schwinger, J., Séférian, R., Stock, C. A., Tagliabue, A., Takano, Y., Tjiputra, J., Toyama, K., Tsujino, H., Watanabe, M., Yamamoto, A., Yool, A., and Ziehn, T.: Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections, Biogeosciences, 17, 3439–3470, https://doi.org/10.5194/bg-17-3439-2020, 2020.
Lachkar, Z., Lévy, M., and Smith, S.: Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity, Biogeosciences, 15, 159–186, https://doi.org/10.5194/bg-15-159-2018, 2018.
Lachkar, Z., Mehari, M., Al Azhar, M., Lévy, M., and Smith, S.: Fast local warming is the main driver of recent deoxygenation in the northern Arabian Sea, Biogeosciences, 18, 5831–5849, https://doi.org/10.5194/bg-18-5831-2021, 2021.
Lacour, L., Llort, J., Briggs, N., Strutton, P. G., and Boyd, P. W.: Seasonality of downward carbon export in the Pacific Southern Ocean revealed by multi-year robotic observations, Nat. Commun., 14, 1278, https://doi.org/10.1038/s41467-023-36954-7, 2023.
Large, W. G., McWilliams, J. C., and Doney, S. C.: Oceanic vertical mixing: A review and a model with a nonlocal boundary layer parameterization, Rev. Geophys., 32, 363–403, https://doi.org/10.1029/94RG01872, 1994.
Lee, C. M., Jones, B. H., Brink, K. H., and Fischer, A. S.: The upper-ocean response to monsoonal forcing in the Arabian Sea: Seasonal and spatial variability, Deep-Sea Res. Pt. II, 47, 1177–1226, https://doi.org/10.1016/S0967-0645(99)00141-1, 2000.
L'Hégaret, P., Lacour, L., Carton, X., Roullet, G., Baraille, R., and Corréard, S.: A seasonal dipolar eddy near Ras Al Hamra (Sea of Oman), Ocean Dynam., 63, 633–659, https://doi.org/10.1007/s10236-013-0616-2, 2013.
Li, N., Zhu, X., Wang, H., Zhang, S., and Wang, X.: Intraseasonal and interannual variability of sea temperature in the Arabian Sea Warm Pool, Ocean Sci., 19, 1437–1451, https://doi.org/10.5194/os-19-1437-2023, 2023.
Li, Q., Webb, A., Fox-Kemper, B., Craig, A., Danabasoglu, G., Large, W. G., and Vertenstein, M.: Langmuir mixing effects on global climate: WAVEWATCH III in CESM, Ocean Model., 103, 145–160, https://doi.org/10.1016/j.ocemod.2015.07.020, 2016.
Li, Q., Bruggeman, J., Burchard, H., Klingbeil, K., Umlauf, L., and Bolding, K.: Integrating CVMix into GOTM (v6.0): a consistent framework for testing, comparing, and applying ocean mixing schemes, Geosci. Model Dev., 14, 4261–4282, https://doi.org/10.5194/gmd-14-4261-2021, 2021.
Li, Z., England, M. H., and Groeskamp, S.: Recent acceleration in global ocean heat accumulation by mode and intermediate waters, Nat. Commun., 14, 1–14, https://doi.org/10.1038/s41467-023-42468-z, 2023.
Liu, L., Huang, R. X., and Wang, F.: Ventilation of a monsoon-dominated ocean: Subduction and obduction in the North Indian Ocean, J. Geophys. Res.-Oceans, 123, 4449–4463, https://doi.org/10.1029/2017JC013719, 2018.
Luo, H., Wang, Z., He, C., Chen, D., and Yang, S.: Future changes in South Asian summer monsoon circulation under global warming: Role of the Tibetan Plateau latent heating, NPJ Clim. Atmos. Sci., 7, 1–9, https://doi.org/10.1038/s41612-024-00653-x, 2024.
Maishal, S.: Unraveling the declining Indian ocean primary productivity and key drivers, Discov. Oceans, 1, 1–18, https://doi.org/10.1007/S44289-024-00018-5, 2024.
McCreary, J. P., Kundu, P. K., and Molinari, R. L.: A numerical investigation of dynamics, thermodynamics and mixed-layer processes in the Indian Ocean, Prog. Oceanogr., 31, 181–244, https://doi.org/10.1016/0079-6611(93)90002-U, 1993.
McCreary, J. P., Yu, Z., Hood, R. R., Vinayachandran, P. N., Furue, R., Ishida, A., and Richards, K. J.: Dynamics of the Indian-Ocean oxygen minimum zones, Prog. Oceanogr., 112–113, 15–37, https://doi.org/10.1016/j.pocean.2013.03.002, 2013.
Mohan, S., Mishra, S. K., Sahany, S., and Behera, S.: Long-term variability of sea surface temperature in the tropical Indian Ocean in relation to climate change and variability, Global Planet. Change, 199, 103436, https://doi.org/10.1016/j.gloplacha.2021.103436, 2021.
Montégut, C. de B., Madec, G., Fischer, A. S., Lazar, A., and Iudicone, D.: Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology, J. Geophys. Res.-Oceans, 109, C12003, https://doi.org/10.1029/2004JC002378, 2004.
Morel, A. and Antoine, D.: Heating rate within the upper ocean in relation to its bio–optical state, J. Phys. Oceanogr., 24, 1652–1665, https://doi.org/10.1175/1520-0485(1994)024<1652:HRWTUO>2.0.CO;2, 1994.
Morrison, J. M.: Inter-monsoonal changes in the T–S properties of the near-surface waters of the Northern Arabian Sea, Geophys. Res. Lett., 24, 2553–2556, https://doi.org/10.1029/97GL01876, 1997.
Niiler, P. and Kraus, E.: One-dimensional models of the upper ocean, in: Modeling and Prediction of the Upper Layers of the Ocean, Adv. Study Inst., Urbino, ltaly, 1975, Pergamon Press, Oxford, 143–172, 1977.
Nisha, P. G., Pranesha, T. S., Vidya, P. J., Ravichandran, M., and Murtugudde, R.: Trend and interannual variability of the Arabian Sea heat content, J. Marine Syst., 242, 103935, https://doi.org/10.1016/j.jmarsys.2023.103935, 2024.
Park, J. Y., Kug, J. S., and Park, Y. G.: An exploratory modeling study on bio-physical processes associated with ENSO, Prog. Oceanogr., 124, 28–41, https://doi.org/10.1016/j.pocean.2014.03.013, 2014.
Parvathi, V., Suresh, I., Lengaigne, M., Izumo, T., and Vialard, J.: Robust projected weakening of winter monsoon winds over the Arabian Sea under climate change, Geophys. Res. Lett., 44, 9833–9843, https://doi.org/10.1002/2017GL075098, 2017.
Phillips, H. E., Tandon, A., Furue, R., Hood, R., Ummenhofer, C. C., Benthuysen, J. A., Menezes, V., Hu, S., Webber, B., Sanchez-Franks, A., Cherian, D., Shroyer, E., Feng, M., Wijesekera, H., Chatterjee, A., Yu, L., Hermes, J., Murtugudde, R., Tozuka, T., Su, D., Singh, A., Centurioni, L., Prakash, S., and Wiggert, J.: Progress in understanding of Indian Ocean circulation, variability, air–sea exchange, and impacts on biogeochemistry, Ocean Sci., 17, 1677–1751, https://doi.org/10.5194/os-17-1677-2021, 2021.
Portela, E., Kolodziejczyk, N., Vic, C., and Thierry, V.: Physical mechanisms driving oxygen subduction in the global ocean, Geophys. Res. Lett., 47, e2020GL089040, https://doi.org/10.1029/2020GL089040, 2020.
Pous, S. P.: Hydrology and circulation in the Strait of Hormuz and the Gulf of Oman – Results from the GOGP99 Experiment: 2. Gulf of Oman, J. Geophys. Res., 109, C12038, https://doi.org/10.1029/2003JC002146, 2004.
Prasad, T. G.: A comparison of mixed-layer dynamics between the Arabian Sea and Bay of Bengal: One-dimensional model results, J. Geophys. Res.-Oceans, 109, C03035, https://doi.org/10.1029/2003JC002000, 2004.
Prasad, T. G. and Ikeda, M.: A numerical study of the seasonal variability of Arabian Sea high-salinity water, J. Geophys. Res.-Oceans, 107, 18-1–18-14, https://doi.org/10.1029/2001JC001139, 2002a.
Prasad, T. G. and Ikeda, M.: The wintertime water mass formation in the northern Arabian Sea: A model study, J. Phys. Oceanogr., 32, 1028–1040, https://doi.org/10.1175/1520-0485(2002)032<1028:TWWMFI>2.0.CO;2, 2002b.
Prasanth, R., Vijith, V., Thushara, V., George, J. V., and Vinayachandran, P. N.: Processes governing the seasonality of vertical chlorophyll-a distribution in the central Arabian Sea: Bio-Argo observations and ecosystem model simulation, Deep-Sea Res. Pt. II, 183, 104926, https://doi.org/10.1016/j.dsr2.2021.104926, 2021.
Qing, S., Cui, T., Tang, J., Song, Q., Liu, R., and Bao, Y.: An optical water classification and quality control model (OC_QC model) for spectral diffuse attenuation coefficient, ISPRS J. Photogramm., 189, 255–271, https://doi.org/10.1016/j.isprsjprs.2022.05.006, 2022.
Rao, R. R., Molinari, R. L., and Festa, J. F.: Evolution of the climatological near-surface thermal structure of the tropical Indian Ocean. 1. Description of mean monthly mixed layer depth, and sea surface temperature, surface current, and surface meteorological fields, J. Geophys. Res., 94, 10801–10815, https://doi.org/10.1029/JC094IC08P10801, 1989.
Rixen, T., Cowie, G., Gaye, B., Goes, J., do Rosário Gomes, H., Hood, R. R., Lachkar, Z., Schmidt, H., Segschneider, J., and Singh, A.: Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean, Biogeosciences, 17, 6051–6080, https://doi.org/10.5194/bg-17-6051-2020, 2020.
Saranya, J. S., Roxy, M. K., Dasgupta, P., and Anand, A.: Genesis and trends in marine heatwaves over the tropical Indian Ocean and their interaction with the Indian summer monsoon, J. Geophys. Res.-Oceans, 127, e2021JC017427, https://doi.org/10.1029/2021JC017427, 2022.
Sasmal, S. K.: Optical classification of waters in the eastern Arabian Sea, J. Indian Soc. Remote, 25, 73–78, https://doi.org/10.1007/BF03025905, 1997.
Schmidtko, S., Stramma, L., and Visbeck, M.: Decline in global oceanic oxygen content during the past five decades, Nature, 542, 335–339, https://doi.org/10.1038/nature21399, 2017.
Shankar, D., Remya, R., Vinayachandran, P. N., Chatterjee, A., and Behera, A.: Inhibition of mixed-layer deepening during winter in the northeastern Arabian Sea by the West India Coastal Current, Clim. Dynam., 47, 1049–1072, https://doi.org/10.1007/s00382-015-2888-3, 2016.
Sharma, S., Ha, K. J., Yamaguchi, R., Rodgers, K. B., Timmermann, A., and Chung, E. S.: Future Indian Ocean warming patterns, Nat. Commun., 14, 1–11, https://doi.org/10.1038/s41467-023-37435-7, 2023.
Shee, A., Sil, S., and Gangopadhyay, A.: Recent changes in the upper oceanic water masses over the Indian Ocean using Argo data, Sci. Rep., 13, 1–14, https://doi.org/10.1038/s41598-023-47658-9, 2023.
Shenoi, S., Shetye, S., Gouveia, A., and Michael, G.: Salinity extrema in the Arabian Sea, University of Hamburg, Germany, 76, 37–49, http://drs.nio.org/drs/handle/2264/2901 (last accesss: 10 March 2025), 1993
Shi, F., Luo, Y., and Xu, L.: Volume and transport of eddy-trapped mode water south of the Kuroshio Extension, J. Geophys. Res.-Oceans, 123, 8749–8761, https://doi.org/10.1029/2018JC014176, 2018.
Singh, S., Valsala, V., Prajeesh, A. G., and Balasubramanian, S.: On the variability of Arabian Sea mixing and its energetics, J. Geophys. Res.-Oceans, 124, 7817–7836, https://doi.org/10.1029/2019JC015334, 2019.
Sun, C., Zhang, A., Jin, B., Wang, X., Zhang, X., and Zhang, L.: Seasonal variability of eddy kinetic energy in the north Indian Ocean, Front. Mar. Sci., 9, 1032699, https://doi.org/10.3389/fmars.2022.1032699, 2022.
Thoppil, P. G.: Mesoscale eddy modulation of winter convective mixing in the northern Arabian Sea, Deep-Sea Res. Pt. II, 216, 105397, https://doi.org/10.1016/j.dsr2.2024.105397, 2024.
Trott, C. B., Subrahmanyam, B., Chaigneau, A., and Roman-Stork, H. L.: Eddy-induced temperature and salinity variability in the Arabian Sea, Geophys. Res. Lett., 46, 2734–2742, https://doi.org/10.1029/2018GL081605, 2019.
Umlauf, L. and Burchard, H.: Second-order turbulence closure models for geophysical boundary layers: A review of recent work, Cont. Shelf Res., 25, 795–827, https://doi.org/10.1016/j.csr.2004.08.004, 2005.
Vijith, V., Vinayachandran, P. N., Thushara, V., Amol, P., Shankar, D., and Anil, A. C.: Consequences of inhibition of mixed-layer deepening by the West India Coastal Current for winter phytoplankton bloom in the northeastern Arabian Sea, J. Geophys. Res.-Oceans, 121, 6583–6603, https://doi.org/10.1002/2016JC012004, 2016.
Vinayachandran, P. N., Kurian, J., and Neema, C. P.: Indian Ocean response to anomalous conditions in 2006, Geophys. Res. Lett., 34, 15602, https://doi.org/10.1029/2007GL030194, 2007.
Weber, T. and Bianchi, D.: Efficient Particle Transfer to Depth in Oxygen Minimum Zones of the Pacific and Indian Oceans, Front. Earth Sci., 8, 567903, https://doi.org/10.3389/FEART.2020.00376, 2020.
Wiggert, J. D., Hood, R. R., Banse, K., and Kindle, J. C.: Monsoon-driven biogeochemical processes in the Arabian Sea, Prog. Oceanogr., 65, 176–213, https://doi.org/10.1016/J.POCEAN.2005.03.008, 2005.
Xu, L., Li, P., Xie, S. P., Liu, Q., Liu, C., and Gao, W.: Observing mesoscale eddy effects on mode-water subduction and transport in the North Pacific, Nat. Commun., 7, 10505, https://doi.org/10.1038/ncomms10505, 2016.
Xu, L., Xie, S. P., and Liu, Q.: Fast and slow responses of the North Pacific mode water and Subtropical Countercurrent to global warming, J. Ocean U. China, 12, 216–221, https://doi.org/10.1007/S11802-013-2189-6, 2013.
Zhan, P., Guo, D., and Hoteit, I.: Eddy-Induced Transport and Kinetic Energy Budget in the Arabian Sea, Geophys. Res. Lett., 47, e2020GL090490, https://doi.org/10.1029/2020GL090490, 2020.
Zhou, Y., Chen, S., Ma, W., Xi, J., Zhang, Z., and Xing, X.: Spatiotemporal variations of the oxycline and its response to subduction events in the Arabian Sea, Front. Mar. Sci., 10, 1171614, https://doi.org/10.3389/fmars.2023.1171614, 2023.
Short summary
Mode water is formed annually and sits between the warm surface water and deeper older waters. In the Arabian Sea, it plays a crucial role in regulating ocean heat and oxygen variability by acting as a doorway between the surface and deeper waters. Using observations and models, we show that its formation is primarily driven by atmospheric forcing, though ocean currents, eddies, and biological heating also influence its life cycle. This water mass contributes up to 40 % of the region's oxygen content.
Mode water is formed annually and sits between the warm surface water and deeper older waters....
