Craig R. Smith, University of Hawaii at Manoa, US
Maria Vernet, Scripps Institution of Oceanography, US
Peter Winsor, University of Alaska, Fairbanks, US
Martin Truffer, University of Alaska, Fairbanks, US
Brian Powell, University of Hawaii at Manoa, US
Mark Merrifield, University of Hawaii at Manoa, US
Clifton Nunnally, University of Hawaii at Manoa, US
Early phytoplankton bloom and large seafloor productivity footprint in Andvord Bay fjord, Antarctica: results from the first FjordEco cruise
Fjords are glacially cut submarine canyons that dissect polar margins. The West Antarctic Peninsula (WAP) has an extensive, rapidly warming system of sub-polar fjords with tidewater glaciers. These fjords appear to be hotspots of biomass and biodiversity, with sustained phytoplankton blooms, massive aggregations of krill and humpback whales, and high abundance and species richness of megabenthos. This spectacular marine life attracts >20,000 tourists to individual WAP fjords each summer. Nonetheless, drivers of high fjord productivity/biodiversity, as well as the sensitivity of WAP fjord ecosystems to climate warming, are very poorly understood. Within the FjordEco Project, we are conducting an integrated field and modeling program to evaluate physical oceanographic processes, glacial inputs, plankton dynamics, and benthic community structure and function in Andvord Bay, a sub-polar WAP fjord, to address two overarching questions: (1) What physical, glaciological, biological and chemical processes interact to enhance fjord productivity and biodiversity? (2) How sensitive are these fjord processes to increased glacial meltwater and sediment inputs expected from climate warming? Our field program will test mechanistic hypotheses concerning oceanographic/glaciological forcing and phytoplankton and benthic community responses, and includes: (1) Deployments of moorings (physical oceanographic, sediment traps, seafloor time-lapse camera), weather stations, and glacial and sea-ice time-lapse cameras to obtain an integrated view of ecosystem processes in the fjord and adjacent Gelarche Strait over 15 months; and (2) spring and fall process cruises using shipboard CTD, towed Acrobat system, AUV glider, and intensive studies of phytoplankton and benthic species composition and production/respiration to elucidate fjord ecosystem structure and function during different seasons. We will then use a coupled physical/biological modeling approach (ROMS/NEMURO) to evaluate drivers of biogeochemical cycles in WAP fjords and to explore their potential sensitivity to enhanced meltwater and sediment inputs.
Here we present results from our spring cruise to Andvord Bay in Nov-Dec 2015 to deploy instruments and evaluate ecosystem processes. The fjord proved physically dynamic, with glacial+sea ice filling/emptying the fjord within days due to tides and katabatic winds. Tabular icebergs with 30-m freeboard roved throughout the fjord, potentially stirring waters to >200 m. The spring phytoplankton bloom was well underway in the fjord by late November while it had not yet begin on the open shelf; the fjord bloom was unexpectedly dominated by cryptomonads which may be favored by meltwater conditions. Primary production was highest over sills in the outer fjord, and the fjord appeared to be exporting meltwater, phytoplankton and nutrients into the Gerlache Strait. Benthic megafaunal abundance was dramatically elevated throughout the fjord relative to Gerlache Strait, with extraordinary abundances occurring <1 km from rapidly flowing (>5 m/d) glacial termini. Sediment community respiration was also 4-fold higher in the fjord than on the open shelf, with the highest rates underlying the zone of high pelagic primary production. Our initial results confirm that Andvord Bay is productive early in the season, especially in the outer fjord, with the benthic footprint of this enhanced productivity extending into the fjord’s innermost recesses.
Theme 2: New ways to study submarine canyons: integrated programs, new technologies and coordinated monitoring efforts
fjord, enhanced biomass, integrated field and modeling program, Antarctica