INSPIRE: Investigating the Role of Mesoscale Processes and Ice Dynamics in Carbon and Iron Fluxes in a Changing Amundsen Sea

Simulated surface chlorophyll in the Amundsen Sea Polynya (OPP-1443657) and sea ice from NSIDC/MODIS

Figure 1: The Amundsen Sea in Dec.2010 (Austral summer). Green shading is the surface chlorophyll from numerical simulations conducted at Old Dominion University (OPP-1443657) and represents algae growing inside ice-free regions (aka “polynyas”). Gray background represents sea ice (ice floating at surface of water) and glacial ice (part of the Antarctic ice sheet) from a satellite (MODIS/NSIDC). North is upward in the figure. ASP: Amundsen Sea Polynya. DIS: Dotson Ice Shelf. CIS: Crosson Ice Shelf. TLT: Thwaites Landfast ice Tongue. B-22A: Large iceberg that calved from the TGT. TGT: Thwaites Glacier Tongue. TIS: Thwaites Ice Shelf. PIP: Pine Island Polynya. PIG: Pine Island Glacier.

Contents:

  1. What is INSPIRE?
  2. Acknowledgment and Disclaimer
  3. Contributors
  4. Outcomes of the project
  5. Figures and videos about INSPIRE and the Amundsen Sea
  6. Other references

What is INSPIRE?

This NSF-funded project (PLR-1443657) united independent, state-of-the-art modeling and field data synthesis efforts to address important unanswered questions about carbon fluxes and iron supply in a key region of the coastal Antarctic. The Amundsen Sea Polynya (ASP), in the remote South Pacific sector of the Southern Ocean, features 1) large intrusions of modified Circumpolar Deep Water (mCDW) onto the continental shelf, 2) the fastest melting ice shelves in Antarctica, 3) the most productive coastal polynya (161 g C/m2) and a large atmospheric CO2 sink, and 4) some of the most rapid declines in seasonal sea ice on Earth. Following on the heels of a highly successful oceanographic field program, the Amundsen Sea Polynya International Research Expedition (ASPIRE; which sampled the ASP with high spatial resolution during the onset of the enormous phytoplankton bloom of 2011 [1]), the project represented a collaboration between ASPIRE senior scientists and an experienced team of physical and a biogeochemical modelers who can use ASPIRE field data to both validate and extend the capabilities of an existing Regional Ocean Modeling System (ROMS, [2]) for the Amundsen Sea [3]. This new effort added biology and biogeochemistry (including features potentially unique to the ASP region) to an existing physical model, allowing us to address key questions about bloom mechanisms that could not be answered by field campaigns or modeling alone. This project generated new insights and hypotheses that will ultimately guide sampling strategies of future field efforts investigating how present and future climate change impacts this important region of the world.

Acknowledgment and Disclaimer

This material on this web page is based upon work supported by the National Science Foundation under Grant Number 1443657. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Contributors

INSPIRE was a collaborative effort between Old Dominion University (ODU; 1443657), University of Georgia (UGA; 1443604), Rutgers University (1443315) and the University of Colorado (1443569). The project involved P.St-Laurent, M.Dinniman and E.Hofmann at ODU, P.Yager and Hilde Oliver at UGA, R.Sherrell at Rutgers University, S.Stammerjohn at U.Colorado, and D.Dickerson at ECU.
Please contact P.St-Laurent (pstlaure@odu.edu) for inquiries about the project.

Outcomes of the project

Summary for the general public

The INSPIRE project investigated a unique region of the coastal Antarctic (the Amundsen Sea Polynya, ASP) characterized by fast-melting glaciers and a very high production of microscopic algae during the summer season. It helped to undercover the inner workings of this region and to progressively reveal the secrets behind its unusually high productivity. One of the most important outcomes of INSPIRE relates to the circulation of the water in the region. The meltwater from the glaciers was found to act like warm air in a shower, rising toward the surface while pulling in water at the bottom. This ‘meltwater pump’ is amplified by the tremendously high glacier melt rates of the Amundsen Sea and influences the water circulation a hundred miles away from the glaciers. The key effect of this pump is that it pulls in bottom water that is rich in iron, transports it upward, and then releases it close to the surface. Computer simulations (akin to those used for weather forecasts) further revealed that the water that is pumped will accumulate over several years in the ASP.

The accumulation of water that is rich in iron has important implications for marine life. Single-celled algae, the backbone of the marine food web, are often deficient in iron in this region of the World Ocean, which can limit their growth rate and therefore the annual ‘yield’ of the region. The meltwater pump partly alleviates this situation in the ASP and contributes to the region’s productivity. This productivity is eventually limited by another factor; the availability of light. Computer simulations revealed that the algae becomes sufficiently abundant in the ASP to partially block the incident sunlight. Ultimately, it is the limited availability of both light and iron that determines the decline of the algae production at the end of the summer season. With this additional insight on the productivity the ASP, the project investigated the fate of the tremendous amount of organic material produced during the summer bloom. This investigation was innovative because it used a state-of-the-art computer simulation representing simultaneously the melt of the glaciers, the circulation of the water and the biological interactions. The simulation revealed that organic matter is transported by the ocean circulation over a distance of a hundred miles before reaching the sea floor or being recycled. This result expands our understanding of the fate of organic matter in the ASP and represents valuable insight for future field efforts.

The INSPIRE project had multiple beneficial impacts for society at large. The computer simulations developed during the course of INSPIRE are shared with other research groups, notably glaciologists studying the contribution of Antarctic glacial melting to global sea level rise. The latter process directly affects coastal communities throughout the world. Moreover, increasing atmospheric CO2 concentrations affect the environment through global warming and ocean acidification. INSPIRE contributed to our understanding of how the ocean, like forests on land, can potentially slow down the increase in atmospheric CO2 concentrations. The goals and outcomes of INSPIRE were communicated in a variety of formats including a magazine article targeting the general public, a website, and multiple publications and presentations for the scientific community. The results of INSPIRE were also integrated into educational activities by a STEM specialist. The activities introduced the students to important physical/biological concepts of marine life and to STEM-related careers in environmental sciences.

Publications

Datasets archived in public repositories

Presentations resulting from INSPIRE

Figures and videos about INSPIRE and the Amundsen Sea

Maps of the Southern Ocean and the Amundsen Sea

Figure 2: (a) Summer chlorophyll climatology for 2002-2013 (shading) in the Southern Ocean (GSFC 2014a) showing higher concentrations on the continental shelves (the scale saturates at 3 mg/m3. The black box is the Amundsen Sea (AS). The Antarctic Circumpolar Current (ACC, black arrow) is bounded by the Sub-Antarctic Front (SAF, outer black line) and the Southern Boundary of the ACC (SBACC, Orsi et al. 1995, inner black line). (b) The Amundsen Sea Model (ASM, St-Laurent et al. 2015) domain with the main ice shelves labeled. The Amundsen Sea Polynya (ASP) is represented with the climatological 15% sea ice concentration line for the month of January (red contour line; from AMSR-E). GIS is Getz Ice Shelf, DIS is Dotson Ice Shelf, CIS is Crosson Ice Shelf, TGT is Thwaites Glacier Tongue, TIS is Thwaites Ice Shelf, PIG is Pine Island Glacier, TIT, is Thwaites Iceberg Tongue, TLT is Thwaites Landfast Tongue, DT is Dotson Trough, CT is Central Trough, MBB is Mid-Bay Bank, ET is Eastern Trough. The topography is from Millan et al. [4] and from RTopo-2.0.1 [5]. The model horizontal resolution is 1.5 km everywhere over the domain to explicitly resolve the mesoscales.

Figure 3: Simulated conditions at the onset of the algal bloom (Nov.1, 2010; year of the ASPIRE cruise). (Top left) Sea ice concentration, (Top right) surface nitrate concentration, (Bottom left) surface particulate organic nitrogen concentration, (Bottom right) surface dissolved iron concentration. For best results, download the video (.webm, .ogv, .mp4) and play it from your device.

Bottom concentration of tracer representing CDW
Figure 4: Numerical tracer representing Circumpolar Deep Water (CDW) intruding over the continental shelf of the Amundsen Sea. A video covering years 2006-2013 is available for download (.webm or .mp4). The tracer is initialized to 1000ppt offshelf where potential temperatures are greater than 0.7C. The video illustrates the pathways and timescales associated with the circulation of CDW (and its associated iron) on the shelf. The model topography is from Millan et al. [4] and RTopo-2.0.1 [5].

Simulated bottom ocean temperature and ice shelf basal melt
Figure 5: Simulated bottom ocean temperature and ice shelf basal melt. Temperature is for Dec.2013 while the basal melt represents an average over years 2006-2013. The model topography is from Millan et al. [4] and RTopo-2.0.1 [5]. The main ice shelves are labeled.

Educational booklet developed for the INSPIRE project
Figure 6: Extract from the educational booklet developed in collaboration with local artists and STEM educators (Carl Twarog being the illustrator). The booklet was used in schools and its efficiency was evaluated by STEM specialist D.Dickerson.

Cover image of research feature on Patricia Yager and the INSPIRE project
Figure 7: The magazine Research Features interviewed co-PI Patricia Yager about the INSPIRE project. This led to an article communicating the project's goals and results to a general audience.

Other references

  1. Yager, P.L., R. M. Sherrell, S. E. Stammerjohn, A.-C. Alderkamp, O. Schofield, E. P. Abrahamsen, K. R. Arrigo, S. Bertilsson, D. L. Garay, R. Guerrero, K. E. Lowry, P.-O. Moksnes, K. Ndungu, A. F. Post, E. Randall-Goodwin, L. Riemann, S. Severmann, S. Thatje, G. L. van Dijken and S. Wilson, 2012. ASPIRE: The Amundsen Sea Polynya International Research Expedition, Oceanography, vol.25(3) p.40-53, doi:10.5670/oceanog.2012.73.
  2. Shchepetkin, A. F. and J. C. McWilliams, 2005. The Regional Oceanic Modeling System (ROMS): A split-explicit, free-surface, topography-following-coordinate oceanic model, Ocean Modelling, vol.9, p.347-404, doi:10.1016/j.ocemod.2004.08.002.
  3. St-Laurent, P., J. Klinck, and M. Dinniman, 2015. Impact of local winter cooling on the melt of Pine Island Glacier, Antarctica, J. Geophys. Res., vol.120(10), p.6718-6732, doi:10.1002/2015jc010709, preprint.
  4. Millan, R., E. Rignot, V. Bernier, M. Morlighem and P. Dutrieux, 2017. Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data, Geophys. Res. Lett., doi:10.1002/2016GL072071.
  5. Schaffer, J., R. Timmermann, J.E. Arndt, S.S. Kristensen, C. Mayer, M. Morlighem and D. Steinhage, 2016. A global, high-resolution data set of ice sheet topography, cavity geometry, and ocean bathymetry. Earth System Science Data, 8(2), 543-557, doi:10.5194/essd-8-543-2016
  6. Powers, J. G., K. W. Manning, D. H. Bromwich, J. J. Cassano and A. M. Cayette, 2012. A decade of Antarctic science support through AMPS, Bulletin of the American Meteorological Society, November, p.1699-1712, doi:10.1175/bams-d-11-00186.1
  7. Mazloff, M.R., P. Heimbach, and C. Wunsch, 2010. An eddy-permitting Southern Ocean State Estimate. J. Phys. Oceanogr., vol.40(5), doi:10.1175/2009jpo4236.1.