Studying Arctic Sea Ice Ecosystem Change

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This article is part of the Fall 2014 issue of the Earth Science Matters Newsletter.

Overview 

map of the Arctic Ocean

Map of Arctic Ocean, showing bathymetry and location of subsurface features and seas. Modified from International Bathymeteric Chart of the Arctic Ocean, courtesy of M. Jakobssen, Stockholm University, (Jakobsson, M., Mayer, L.A., Bringensparr, C. et al. The International Bathymetric Chart of the Arctic Ocean Version 4.0. Sci Data 7, 176 (2020). https://doi.org/10.1038/s41597-020-0520-9)

(Public domain.)

The Arctic is undergoing a rapid environmental transformation such that the Arctic is warming faster than other regions and loss of snow and ice cover is causing more solar radiation to be absorbed, compounding the warming and melting. Such changes have the potential to alter terrestrial and marine habitats and ecosystems, affect permafrost and carbon cycling, and affect people, industry, and commerce in the Arctic. 

Arctic sea-ice loss and ecosystem change 

Sea ice is a critical feature of the Arctic Ocean and surrounding regions. Mammals and birds rely on sea ice for resting, hunting, and reproduction. Alaskan native communities depend on ice for subsistence fishing, whale and seal hunting. The annual cycle of Arctic and subarctic springtime ice melt initiates phytoplankton blooms that drive annual ecosystem functioning. Many regions in the Arctic, such as the Chukchi and Bering Seas off Alaska, are experiencing earlier spring sea-ice retreat and later autumn sea-ice formation affecting the timing of food and habitat availability for animals and humans.

Since 1979, when satellite-based measurements began, Arctic sea ice cover and thickness has been decreasing in most regions of the Arctic and researchers have also documented changes in the abundance and distribution of key marine species. Although there is a large amount of uncertainty in predictions of future sea ice, there is nonetheless concern that these trends will continue. As a consequence, the United States has developed a National Strategy for the Arctic Region which positions the country for future challenges and opportunities in the Arctic. Similarly, the Department of Defense Arctic Strategy addresses potential security issues stemming from Arctic environmental change.

Paleo-records help understand Arctic ecosystem variability 

Most instrumental records of Arctic ecosystems extend back only a few decades, and historical climate recordkeeping began just over a century ago. This short time frame of study limits our understanding of natural climate, sea-ice and marine ecosystem variability. To more fully understand the baseline variability in Arctic climate, researchers use paleoclimate records preserved in natural archives such as sediments deposited in lakes and oceans, tree rings, glacial ice and speleothems. By analyzing paleo-records from critical sites in the Arctic Ocean, researchers are developing a more complete understanding of regional patterns of sea-ice variability over decadal, centennial and millennial time scales.

How do scientists reconstruct long climate records? 

scanning electron microscope image of ostracode

Scanning electron microscope photo of shell of the ostracode Acetabulastoma, which inhabits perennial sea ice and whose fossils from sediment cores provide a history of sea ice in the Arctic Ocean and adjacent seas.

(Credit: Laura Gemery, USGS. Public domain.)

Researchers use a variety of proxy methods to reconstruct past climates and environments in the Arctic Ocean and other regions. Proxies typically involve measurements of physical, biological or chemical features of sediments that have accumulated over thousands to millions of years. For example, reconstructing past changes in Arctic Ocean temperature, circulation, sea level and sea ice involves the use of small microfossil groups including ostracodes, a group of small, shelled Crustacea, and foraminifera, single-celled protists that secrete calcareous shells. The ability to use ostracodes, foraminifera and other biological groups to reconstruct past environments relies on understanding their geographic and depth distribution and other ecological requirements in the modern Arctic environment. Especially important are the temperature, depth, salinity, and oxygen levels that species can tolerate. Similarly, the chemistry of microfossil shells and the sediment in which they are preserved yields quantitative information about past ocean temperature, salinity, sea ice cover, and ocean chemistry. On land areas, pollen and various lake-dwelling microfossil groups are used to reconstruct terrestrial environmental change. The USGS Arctic Paleoceanography website provides more information about paleoclimatology and the Arctic’s climate history.

Arctic research cruises 

Given the challenges of working in the Arctic, scientific expeditions are usually carried out aboard specially outfitted research vessels. The USGS and other federal agencies have operated cruises to the Arctic since the 1950s. Early research missions focused on surveying the ocean floor and creating seismic profiles to collect information about energy resources. In addition, USGS and other agencies also conducted expeditions to map the bathymetry of the seafloor and gather geophysical data about the geology and composition of the sediments and seafloor, including oceanographic measurements. Collectively these cruises provide samples and data that can be studied for many scientific purposes.

Case Study: 2012-2013 Chukchi Sea Cruises 

Image: US Coast Guard Cutter Healy

USCGC Healy conducted BOEM- and NSF- sponsered cruises during summer 2012 and 2013 in which USGS scientists participated.

(Credit: Tom Cronin, USGS. Public domain.)

During the 2012 and 2013 field seasons, the Bureau of Ocean and Energy Management (BOEM) sponsored research expeditions on the United States Coast Guard (USCG) Icebreaker Healy to the Hanna Shoal region of the Chukchi Sea to examine ecosystem trophic structure, sediments, and anthropogenic chemicals. Led by chief scientists Drs. Lee Cooper and Jackie Grebmeier, University of Maryland, and Dr. Kenneth Dunton, University of Texas at Austin, the Hanna Shoal cruises included scientists from government organizations including USGS and several academic institutions conducting multi-disciplinary studies of marine life in the Hanna Shoal region.

These cruises collect baseline data on biological resources that may be at risk from energy exploration and other human activities in the Arctic. Scientists aboard the Healy aimed to document the biodiversity and distribution of zooplankton and benthic invertebrates, such as clams and crabs. Planktonic and benthic organisms are essential links in marine sea-ice ecosystems that also support populations of sea birds and marine mammals like walrus, seals and gray whales. 

Sediment is collected in a variety of ways during research cruises. Some devices, such as a Van Veen grab sampler, collect only the uppermost seafloor sediment, whereas longer coring devices capture deeper columns of sediment that provide records of the past hundreds to thousands of years. On board, scientists wash and sieve samples to isolate the organisms from sediment. Additional study is then conducted after the cruise in government and university laboratories where scientists sort, identify and count faunal collections for studies of changes in ecosystem structure and biodiversity. 

scientists prepare to deploy Van Veen grab sampler

The Van Veen grab sampler is designed to recover sediment and associated faunas from the seafloor. These surface sediments are used to assess faunal changes due to climate-driven changes in temperature, salinity, productivity, and sea ice.

(Credit: Laura Gemery, USGS. Public domain.)

One focus of USGS research is the documentation of the distribution and composition of benthic ostracode assemblages in the Bering and Chukchi Seas during the last 40 years. Because ostracode shells are preserved long after the animal’s soft parts degrade, researchers can acquire data from archived surface sediments from prior Arctic cruises dating back to the 1960s. Analysis of ostracode assemblages show that changes in the abundance of dominant species appear to be related to changes in temperature and sea ice over the last few decades. In addition to documenting recent ecosystem changes, these faunal analyses provide baseline ecological data that can be used in future studies of the response of Arctic ecosystems to long-term climate variability and change.

Future Arctic Research 

Continued observation and paleoclimate reconstruction at various temporal scales will improve scientific understanding of the Arctic’s natural variability. More generally, scientific investigation in the Arctic Ocean can help establish the impacts of climate-related environmental change that help decision-makers and planners in developing mitigation and adaptation plans for changes in the future.

For additional information on USGS research on Arctic paleoclimatology: https://www.usgs.gov/ecosystems/climate-research-development-program/science/paleoclimate

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