EGU2020-22442, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-22442
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Long time-series of export fluxes in the western Ross Sea (Antarctica)

Patrizia Giordano1, Federico Giglio1, Mariangela Ravaioli2, Marco Capello3, Laura Cutroneo3, Robert B. Dunbar4, David A. Mucciarone4, Walker O. Smith5, Clara Manno6, and Leonardo Langone1
Patrizia Giordano et al.
  • 1CNR, Institute of Polar Sciences, Bologna, Italy
  • 2CNR, Institute of Marine Sciences, Bologna, Italy
  • 3University of Genoa, DISTAV, Genoa, Italy
  • 4Stanford University, Stanford, USA
  • 5Virginia Institute of Marine Science, Gloucester Point, USA
  • 6BAS, British Antarctic Survey, Cambridge, UK

The export of particulate organic carbon (POC) from the sea surface is an essential part of the biological pump. Export fluxes are the result of what is produced in surface water and how much is consumed during particle sinking in the water column. In the Ross Sea, fluxes of POC and total mass are well correlated implying that particle fluxes are dominated by biogenic debris.

Here, we report new and reference data of vertical particle fluxes to below the productive layer obtained on decadal time scales (1990-2017) by automatic sediment traps tethered to moorings in the western Ross Sea (Antarctica). Compilation of all data available in the Ross Sea (23 sites, >1000 samples) shows that annual POC fluxes to below 200 m average 4.4±3.3 g C m-2  y-1. Particle fluxes are relatively low when primary production is high (spring-summer) followed by enhanced sedimentation in late summer-fall. The high degree of decoupling between production and sedimentation is unusual compared to records of Antarctic Peninsula and may represent low grazing rates. Furthermore, data exhibit a large interannual variability and a decreasing trend over time, with a clear shift after 2000. Do the reduced export fluxes depend on lower biological production, enhanced OM consumption, or other processes (e.g., lateral transfer of biogenic particles outside the study area)?

Satellite observations allow us to reconstruct the seasonal and interannual change of chlorophyll biomass, and sea ice extent and duration. Water temperature recorded at mid-depth is used to monitor the different intrusion over time of CDW, the main driver of temporal variability of Fe supply for the Ross Sea. Time series of particle fluxes, chlorophyll, sea ice cover and mid-depth temperature will be compared in order to test if the recent reduction of downward particle fluxes depend on primary production changes.

How to cite: Giordano, P., Giglio, F., Ravaioli, M., Capello, M., Cutroneo, L., Dunbar, R. B., Mucciarone, D. A., Smith, W. O., Manno, C., and Langone, L.: Long time-series of export fluxes in the western Ross Sea (Antarctica), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22442, https://doi.org/10.5194/egusphere-egu2020-22442, 2020

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Presentation version 4 – uploaded on 05 May 2020
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  • CC1: Comment on EGU2020-22442, Cathryn Wynn-Edwards, 07 May 2020

    Dear Patrizia Giordano,

    thank you for presenting your interesting work on the particle fluxes of the Ross Sea. I noticed that the sample number / year was highly variable across the time series and wondered whether there was a systematic bias in the number of samples / year?

    Regards,

    Cathryn Wynn-Edwards

    • AC1: Reply to CC1, Patrizia Giordano, 07 May 2020

      Thanks Cathryn for your question,

      The number of samples per year depends on the number of working moorings  coming from different research projects.

      I do not see any correlation between the number of samples/years and particle fluxes. On the contrary, we suspected that the decreasing over time could depend on the spatial distribution of mooring sites. After 2000, the only active moorings were in the northern part of the continental shelf

      For this reason, we prefer to focus on a specific mooring, the mooring B in the Joides basin

  • CC2: Relation to sea-ice changes, Alexander Haumann, 15 May 2020

    Very interesting results, Patrizia! Thanks for sharing these in your display. I found especially the strong long-term decline in the POC flux in the most southern Ross Sea very interesting. Could this be related to the coastal polynya opening or the overall sea-ice production rates in this area, which would influence e.g. vertical mixing?

    • AC2: Reply to CC2, Patrizia Giordano, 19 May 2020

      Dear Alex,

      Thank you for your question and for the interesting session and stimulating discussion. Although I prefer to meet people face-to-face,  as happens in a classic congress, I found the organization of this virtual meeting very constructive.

      I am not sure to have well understood your question. Theoretically, vertical mixing promotes a faster transfer time of organic particles settling from the uppermost water column to the interior of the ocean and a reduced consumption/remineralization. Hence, reduced export fluxes should imply a higher water stratification. From references of the Ross Sea, this does not seem confirmed during the period 1995-2016.

      In your paper of 2016, you suggested an increasing sea-ice export over time from the Ross Sea by southerly winds and a higher polynya efficiency. On the contrary, the duration of ice-free days on the Ross Sea continental shelf has decreased by over 2 months over the past three decades [Stammerjohn et al., 2012], which may decrease the annual productivity and the role in the ecosystem of groups that rely on open water (Smith et al., 2014). We suspect that the main reason of POC flux decrease depends on an overall decline of biological production. We will work to find further evidence of PP reduction to better frame our data in a specific publication, but taking into account all other processes that can have impacted the biological pump efficiency.

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