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Ecosystems under pressure:

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Projections of ocean physics and biogeochemistry

demand adoption of Weddell Sea Marine Protected Area

Cara Nissen

In collaboration with Judith Hauck, Ralph Timmermann, Mario Hoppema, Nikki Lovenduski, Cassandra Brooks

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Bergen, May 2023

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A planned network of Antarctic Marine Protected Areas to sustain biodiversity

  • Ross Sea: adopted
  • South Orkney

Islands: adopted

Weddell Sea:

proposed

East Antarctic:

proposed

Antarctic

Peninsula:

proposed

  • increase resilience

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  • prohibit (commercial) fishing
  • Commission for the Conservation of Antarctic Marine Living Resources

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  • Evaluation of effectiveness requires understanding of changes in environmental stressors

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Brooks et al. (2020)

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Key organisms of the high-latitude Southern Ocean ecosystem

https://www.nytimes.com/2022/01/13/science/icefish-antarctica-eggs-colony.html

Purser et al. (2022)

Benthos

Pelagic

Lower and

mid-trophic levels

Upper trophic levels

Currently of interest

to fisheries

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Tool: FESOM1.4-REcoM2 with ice-shelf cavities

How are environmental stressors projected to change over the 21st century?

Simulations from 1950-2100

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Forced with atmospheric output from the AWI Climate Model

(Semmler et al., 2020; Nissen et al., 2022)

Four emission scenarios:

  • SSP1-2.6
  • SSP2-4.5
  • SSP3-7.0
  • SSP5-8.5

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The Weddell Sea today: a climate-change refuge

February 2023

FESOM, 1990s

Weddell Sea

Amundsen Sea

  • Dense-shelf regime: continental shelf is largely shielded from inflow of warm, oxygen-poor Circumpolar Deep Water
  • Providing a refuge for cold-adapted organisms and those relying on the presence of sea ice in any of their life cycle stages
  • Higher summer sea-ice cover than other high-latitude sectors

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The future: a regime shift under the highest-emission scenario

  • Highest emission scenarios: hardly any summer sea ice cover left

enhanced CDW inflow

shielded from CDW inflow

warm shelf

dense shelf

  • Highest emission scenarios: shift to warm-shelf regime

high emission

low emission

  • Highest emission scenarios: enhanced on-shelf heat transport

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FT

RD

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The future: consequences of enhanced on-shelf CDW transport

Pronounced bottom warming and deoxygenation along the slope and in Filchner Trough

Impacts on marine organisms?

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The future: ocean acidification (OA)

Continental shelf more severely affected than open ocean

More effective

vertical mixing!

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The future: ubiquitous aragonite undersaturation

whole MPA

Substantial calcite undersaturation under highest-emission scenario

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Summary: Making a case for the Weddell Sea MPA

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Under all but the lowest-emission scenario, organisms on the Weddell Sea continental shelf will be exposed to pronounced warming, deoxygenation (benthos), acidification, and sea-ice retreat.

Figure provided by Cassandra Brooks

Commercial fishing activities in the Weddell Sea are still limited today (largely due to its inaccessibility).

Besides mitigation efforts, establishing the Weddell Sea MPA is a critical piece in reducing the pressure on marine ecosystems.

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Cited literature

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989 (project COMFORT, Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points). The work reflects only the author’s/authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.

Contact:

cara.nissen@colorado.edu

Brooks, C. M., Chown, S. L., Douglass, L. L., Raymond, B. P., Shaw, J. D., Sylvester, Z. T., & Torrens, C. L. (2020). Progress towards a representative network of Southern Ocean protected areas. PLOS ONE, 15(4), e0231361. https://doi.org/10.1371/journal.pone.0231361

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Nissen, C., Timmermann, R., Hoppema, M., Gürses, Ö., & Hauck, J. (2022). Abruptly attenuated carbon sequestration with Weddell Sea dense waters by 2100. Nature Communications, 13(1), 3402. https://doi.org/10.1038/s41467-022-30671-3

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Purser, A., Hehemann, L., Boehringer, L., Tippenhauer, S., Wege, M., Bornemann, H., Pineda-Metz, S. E. A., Flintrop, C. M., Koch, F., Hellmer, H. H., Burkhardt-Holm, P., Janout, M., Werner, E., Glemser, B., Balaguer, J., Rogge, A., Holtappels, M., & Wenzhoefer, F. (2022). A vast icefish breeding colony discovered in the Antarctic. Current Biology, 32(4), 842-850.e4. https://doi.org/10.1016/j.cub.2021.12.022

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Semmler, T., Danilov, S., Gierz, P., Goessling, H. F., Hegewald, J., Hinrichs, C., Koldunov, N., Khosravi, N., Mu, L., Rackow, T., Sein, D. V., Sidorenko, D., Wang, Q., & Jung, T. (2020). Simulations for CMIP6 With the AWI Climate Model AWI‐CM‐1‐1. Journal of Advances in Modeling Earth Systems, 12(9), 1–34. https://doi.org/10.1029/2019MS002009

In review: