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Paper title Key drivers of interannual variability in the Laptev Sea from satellite based sea surface salinity
Authors
  1. Phoebe Hudson University of Edinburgh Speaker
  2. Adrien Martin National Oceanography Centre (NOC)
  3. Athanasios Angeloudis University of Edinburgh
  4. Simon Josey National Oceanography Centre, Southampton, UK
  5. Alice Marzocchi
Form of presentation Poster
Topics
  • A8. Ocean
    • A8.07 Oceanographic Change of the Arctic Ocean From Space
Abstract text Whilst the Arctic Ocean is relatively small, containing only 1% of total ocean volume, it receives 10% of global river runoff. This river runoff is a key component of the Arctic hydrological cycle, providing significant freshwater exchange between land and the ocean. Of this runoff, Russian rivers alone contribute around half of the total river discharge, or a quarter of the total freshwater to the Arctic Ocean, predominantly to the Kara and Laptev Seas. In these seas, inflowing riverine freshwater remains at the surface, helping to form the cold, fresh layer that sits above inflowing warm and salty Atlantic Water; this sets up the halocline that governs Eurasian shelf sea, and wider Arctic Ocean, stratification. This fresh surface layer prevents heat exchange between the underlying Atlantic Water and the overlying sea ice, limiting sea ice melt and strengthening the existing sea ice barrier to atmosphere-ocean momentum transfer. However, the processes that govern variability in riverine freshwater runoff and its interactions with sea ice are poorly understood and are key to predicting the future state of the Arctic Ocean. Understanding these processes is particularly important in the Laptev Sea as a source region of the Transpolar Drift and a key region of sea ice production and deep water formation (Reimnitz et al., 1994).

Over most of the globe, L-band satellite acquisitions of sea surface salinity (SSS), such as from Aquarius (2011–2015), SMOS (2010- present), and SMAP (2015-present), provide a new tool to study freshwater storage and transport. However, the low sensitivity of L-band signal in cold water and the presence of sea ice makes retrievals at high latitudes a challenge. Nevertheless, retreating Arctic sea ice cover and continuous progress in satellite product development make the satellite based SSS measurements of great value in the Arctic. This is particularly evident in the Laptev Sea, where gradients in SSS are strong and in situ measurements are sparse. Previous work has demonstrated a good consistency of satellite based SSS data against in situ measurements, enabling greater confidence in acquisitions and making satellite SSS data a truly viable potential in the Arctic (Fournier et al., 2019; Supply et al., 2020).

This study combines satellite based SSS data, in-situ observations and reanalysis products to study the roles of Lena river discharge, ocean circulation, vertical mixing and sea ice cover on interannual variability in Laptev Sea dynamics. Comparison of two SMOS products, SMOS LOCEAN CEC L3 Arctic v1.1 and SMOS BEC Arctic L3 v3.1, and two SMAP SSS products, SMAP JPL L3 v5.04.2 and SMAP RSS L3 v4.03 were considered. Whilst the general patterns of salinity are broadly similar in all products, their patterns differ interannualy, with particular discrepancies in magnitude. Interannual variability in the LOCEAN SMOS SSS closely resembles that in both SMAP products, most notably in the magnitude and direction of Lena river plume propagation. However, the mean state of SMAP RSS SSS is much fresher than the other products. Comparison against TOPAZ reanalysis highlights similar interannual pattern with both SMAP products and SMOS LOCEAN, but with lower amplitude. The close resemblance of the SMOS CEC LOCEAN and the SMAP products gives confidence in using the full SMOS LOCEAN timeseries (2012-present) to study interannual variability on a 10-year time scale. The full SMOS LOCEAN timeseries shows that two years (2018 and 2019) stand out as having a much larger, fresher river plume than other years. However, the larger plume in these years doesn’t appear to be caused by increases in Lena river runoff. Numerical model output, in-situ data and satellite products are used to study the cause of this variability.



Bibliography
Fournier, S., Lee, T., Tang, W., Steele, M., Olmedo, E., 2019. Evaluation and Intercomparison of SMOS, Aquarius, and SMAP Sea Surface Salinity Products in the Arctic Ocean. Remote Sens. 11, 3043. https://doi.org/10.3390/rs11243043
Reimnitz, E., Dethleff, D., Nürnberg, D., 1994. Contrasts in Arctic shelf sea-ice regimes and some implications: Beaufort Sea versus Laptev Sea. Mar. Geol., 4th International Conference on Paleoceanography (ICP IV) 119, 215–225. https://doi.org/10.1016/0025-3227(94)90182-1
Supply, A., Boutin, J., Vergely, J.-L., Kolodziejczyk, N., Reverdin, G., Reul, N., Tarasenko, A., 2020. New insights into SMOS sea surface salinity retrievals in the Arctic Ocean. Remote Sens. Environ. 249, 112027. https://doi.org/10.1016/j.rse.2020.112027