Archive for ice cover

Ice sheets mobilize trace elements for export downstream

Posted by mmaheigan 
· Thursday, January 7th, 2021 

Trace elements are essential micronutrients for life in the ocean and also serve as valuable fingerprints of chemical weathering. The behaviour of trace elements in the ocean has gained interest because some of these elements are found at vanishingly low concentrations that limit ecosystem productivity. Despite delivering >2000 km3 yr-1 of freshwater to the polar oceans, ice sheets have largely been overlooked as major trace element sources. This is partly due to a lack of data on meltwater endmember chemistry beneath and emerging from the Greenland and Antarctic ice sheets, which cover 10% of Earth’s land surface area, and partly because meltwaters were previously assumed to be dilute compared to most river waters.

In a study published in PNAS, authors analysed the trace element composition of meltwaters from the Mercer Subglacial Lake, a hydrologically active subglacial lake >1000 m below the surface of the Antarctic Ice Sheet, and a meltwater river emerging from beneath a large outlet glacier of the Greenland Ice Sheet (Leverett Glacier). These subglacial meltwaters (i.e., water travelling along the ice-rock interface beneath an ice mass) contained much higher concentrations of trace elements than anticipated. For example, typically immobile elements like iron and aluminium were observed in the dissolved phase (<0.45 µm) at much higher concentrations than in mean river or open ocean waters (up to 20,900 nM for Fe and 69,100 nM for Al), but exhibited large size fractionation between colloidal/nanoparticulate (0.02 – 0.45 µm) and soluble (<0.02 µm) size fractions (Figure 1). Subglacial physical and biogeochemical weathering processes are thought to mobilize many of these trace elements from the bedrock and sediments beneath ice sheets and export them downstream. Antarctic subglacial meltwaters were more enriched in dissolved trace elements than Greenland Ice Sheet outflow, which is likely due to longer subglacial residence times, lack of dilution from surface meltwater inputs, and differences in underlying sediment geology.

These results indicate that ice sheet systems can mobilize large quantities of trace elements from the land to the ocean and serve as major contributors to regional elemental cycles (e.g., coastal Southern Ocean). In a warming climate with increasing ice sheet runoff, subglacial meltwaters will become an increasingly dynamic source of micronutrients to coastal oceanic ecosystems in the polar regions.

Figure caption: Leverett Glacier (Greenland Ice Sheet) and Mercer Subglacial Lake (Antarctic Ice Sheet) dissolved elemental concentrations (<0.45 µm) normalized to mean non-glacial riverine trace element concentrations (Gaillardet et al., 2014) and major element concentrations (Martin and Meybeck, 1979). Grey regions indicate ±50 % of the riverine mean. Although major elements can be significantly depleted compared to non-glacial rivers, trace elements are commonly similar to or enriched.

 

Authors:
Jon R. Hawkings (Florida State Univ and German Research Centre for Geosciences)
Mark L. Skidmore (Montana State Univ)
Jemma L. Wadham (Univ of Bristol, UK)
John C. Priscu (Montana State Univ)
Peter L. Morton (Florida State Univ)
Jade E. Hatton (Univ of Bristol, UK)
Christopher B. Gardner (Ohio State Univ)
Tyler J. Kohler (École Polytechnique Fédérale de Lausanne, Switzerland)
Marek Stibal (Charles University, Prague, Czech Republic)
Elizabeth A. Bagshaw (Cardiff Univ, UK)
August Steigmeyer (Montana State Univ)
Joel Barker (Univ of Minnesota)
John E. Dore (Montana State Univ)
W. Berry Lyons (Ohio State Univ)
Martyn Tranter (Univ of Bristol, UK)
Robert G. M. Spencer (Florida State Univ)
SALSA Science Team

Sea ice loss and the changing Arctic carbon cycle

Posted by mmaheigan 
· Friday, September 18th, 2020 

Loss of Arctic Ocean ice cover is altering the carbon cycle in ways that are not well understood. Effectively “popping the top off” the Arctic Ocean, ice loss exposes the sea surface to warming and exchange of CO2 with the atmosphere. These processes are expected to increase CO2 levels in the Arctic Ocean, changing its contribution to the global carbon cycle, but limited data collection in the region has thus far precluded the establishment of a clear relationship between CO2 and ice cover. In a recent study published in Geophysical Research Letters, authors report on observed partial pressure of CO2 (pCO2) trends from several years of data collection in the surface waters of the Canada Basin of the Arctic Ocean. These data show that the pCO2 is higher during years when ice cover is low. Uptake of atmospheric CO2 and heating are the primary sources of the CO2 increase, with only a small counteracting offset from biological production. These processes vary significantly from year to year, masking the likely increase in pCO2 over time. Based on these results, we can expect that, while the Arctic Ocean has thus far been a significant sink for atmospheric CO2, if ice loss continues the uptake of CO2 will diminish in coming years.

Figure caption: Sea surface pCO2 increases with decreasing ice concentration (left), determined using the mean of spatially gridded data. The sea surface pCO2 data were collected on five research cruises on the Canadian icebreaker, CCGS Louis S. St-Laurent, from 2012 to 2017 (shown at right for 2017). The pCO2 levels are indicated by the color along the ship cruise track (right color bar). The dark shading (left color bar) represents sea ice concentration averaged from the daily satellite data collected during the cruise.

Authors:
Michael DeGrandpre (University of Montana-Missoula)
Wiley Evans (Hakai Institute)
Mary-Louise Timmermans (Yale University)
Richard Krishfield (Woods Hole Oceanographic Institution)
Bill Williams (Institute of Ocean Sciences)
Michael Steele (University of Washington)

Satellite Laser Lights Up Polar Research

Posted by mmaheigan 
· Thursday, April 13th, 2017 

What controls annual cycles and interannual changes in polar phytoplankton biomass? Answers to this question are now emerging from a satellite light detection and ranging (lidar) sensor, which can observe the polar oceans throughout the extensive periods when measurements from traditional passive ocean color sensors are impossible. The new study uses active lidar measurements from the CALIOP satellite sensor to construct complete decade-long record of phytoplankton biomass in the northern and southern polar regions. Results of the study show that annual cycles in biomass are driven by rates of acceleration and deceleration in phytoplankton division, with bloom termination coinciding with maximum division rates irrespective of whether nutrients are exhausted. The study further shows that interannual differences in bloom strength can be quantitatively related to the difference between the winter minimum to summer maximum in division rates. Finally, the analysis indicated that ecological processes had a greater impact than ice cover changes on integrated polar zone phytoplankton biomass in the north, whereas ice cover changes were the dominant driver in the south polar zone. Despite being designed for atmospheric research, CALIOP has provided the first demonstration that active satellite lidar measurements can yield important new insights on plankton ecology in the climate sensitive polar regions. This proof-of-concept creates a foundation for a future ocean-optimized sensor with water-column profiling capabilities that would launch a new lidar era in satellite oceanography.

 

 

Authors:

Michael J. Behrenfeld (Oregon State Univ.)
Yongxiang Hu (NASA Langley Research Center)
Robert T. O’Malley (Oregon State Univ.)
Emmanuel S. Boss (Univ. Maine)
Chris A. Hostetler (NASA Langley Research Center)
David A. Siegel (Univ. California Santa Barbara)
Jorge Sarmiento (Princeton Univ.)
Jennifer Schulien (Oregon State Univ.)
Johnathan W. Hair (NASA Langley Research Center)
Xiaomei Lu (NASA Langley Research Center)
Sharon Rodier (NASA Langley Research Center)
Amy Jo Scarino (NASA Langley Research Center)

International team of researchers reports ocean acidification is spreading rapidly in the western Arctic Ocean

Posted by mmaheigan 
· Thursday, March 30th, 2017 

The Arctic Ocean is particularly sensitive to climate change and ocean acidification such that aragonite saturation state is expected to become undersaturated (Ωarag <1) there sooner than in other oceans. However, the extent and expansion rate of ocean acidification (OA) in this region are still unknown.

In the March 2017 issue of Nature Climate Change, Qi et al. show that, between 1994 and 2010, low Ωarag waters have expanded northwards at least 5º, to 85ºN, and deepened from 100 m to 250 m depth. Data from multiple trans-western Arctic Ocean cruises show that Ωarag<1 water has increased in the upper 250 m from 5 to 31% of the total area north of 70ºN. Tracer data and model simulations suggest that increased transport of Pacific Winter Water (which is already acidified due to both natural and anthropogenic sources), driven by sea-ice retreat and the circulation changes, are primarily responsible for the expansion, while local carbon recycling and anthropogenic CO2 uptake have also contributed. These results indicate more rapid acidification is occurring in the Arctic Ocean, two to four times faster than the Pacific and Atlantic Oceans, with the western Arctic Ocean the first open-ocean region with large-scale expansion of “acidified” water directly observed in the upper water column.

The rapid spread of ocean acidification in the western Arctic has implications for marine life, particularly clams, mussels and pteropods that may have difficulty building or maintaining their shells in increasingly acidified waters. The pteropods are part of the Arctic food web and important to the diet of salmon and herring. Their decline could affect the larger marine ecosystem.

Authors:
Richard A. Feely (NOAA Pacific Marine Environmental Laboratory)
Leif G. Anderson (Univ. of Gothenburg)
Heng Sun (SOA Third Institute of Oceanography)
Jianfang Chen (SOA Second Institute of Oceanography
Min Chen (Univ. of Delaware)
Liyang Zhan (SOA Third Institute of Oceanography)
Yuanhui Zhang (SOA Third Institute of Oceanography)
Wei-Jun Cai (Univ. of Delaware, Univ. of Georgia)

Filter by Keyword

234Th disequilibrium abundance acidification africa air-sea interactions air-sea interface algae alkalinity allometry ammonium AMOC anoxia anoxic Antarctic anthro impacts anthropogenic carbon aquaculture aragonite saturation arctic Argo arsenic artificial seawater Atlantic Atlantic modeling atmospheric carbon atmospheric CO2 atmospheric nitrogen deposition authigenic carbonates autonomous platforms bacteria BATS benthic bgc argo bio-go-ship bio-optical bioavailability biogeochemical cycles biogeochemical cycling biogeochemical models biogeochemistry Biological Essential Ocean Variables biological pump biological uptake biophysics bloom blooms blue carbon bottom water boundary layer buffer capacity C14 CaCO3 calcification calcite carbon-climate feedback carbon-sulfur coupling carbon budget carbon cycle carbon dioxide carbon export carbon sequestration carbon storage Caribbean CCA CCS changi changing marine ecosystems changing marine environments changing ocean chemistry chemical oceanographic data chemical speciation chemoautotroph chesapeake bay chl a chlorophyll circulation climate change climate variability CO2 CO2YS coastal darkening coastal ocean cobalt Coccolithophores community composition conservation cooling effect copepod coral reefs CTD currents cyclone data data access data management data product Data standards DCM dead zone decadal trends decomposers decomposition deep convection deep ocean deep sea coral deoxygenation depth diagenesis diatoms DIC diel migration dimethylsulfide dinoflagellate discrete measurements dissolved inorganic carbon dissolved organic carbon DOC DOM domoic acid dust DVM earth system models ecology ecosystems ecosystem state eddy Education Ekman transport emissions ENSO enzyme equatorial regions error ESM estuarine and coastal carbon estuarine and coastal carbon fluxes estuary euphotic zone eutrophication evolution export export fluxes export production EXPORTS extreme events extreme weather events faecal pellets filter feeders filtration rates fire fish Fish carbon fisheries floats fluid dynamics fluorescence food webs forage fish forams freshening freshwater frontal zone fronts functional role future oceans geochemistry geoengineering geologic time GEOTRACES glaciers gliders global carbon budget global ocean global warming go-ship grazing greenhouse gas Greenland groundwater Gulf of Maine Gulf of Mexico Gulf Stream gyre harmful algal bloom high latitude human food human impact hurricane hydrogen hydrothermal hypoxia ice age ice cores ice cover industrial onset inverse circulation ions iron iron fertilization isotopes jellies katabatic winds kelvin waves krill kuroshio laboratory vs field land-ocean continuum larvaceans lateral transport LGM lidar ligands light light attenuation lipids mangroves marine carbon cycle marine heatwave marine snowfall marshes Mediterranean meltwater mesopelagic mesoscale metagenome metals methane methods microbes microlayer microorganisms microscale microzooplankton midwater mixed layer mixed layers mixotrophy modeling models mode water molecular diffusion MPT multi-decade n2o NAAMES NASA NCP net community production net primary productivity new ocean state new technology Niskin bottle nitrate nitrogen nitrogen fixation nitrous oxide north atlantic north pacific nuclear war nutricline nutrient budget nutrient cycling nutrient limitation nutrients OA ocean-atmosphere ocean acidification ocean acidification data ocean carbon uptake and storage ocean color ocean observatories ocean warming ODZ oligotrophic omics OMZ open ocean optics organic particles oscillation overturning circulation oxygen pacific paleoceanography particle flux pCO2 PDO peat pelagic PETM pH phenology phosphorus photosynthesis physical processes physiology phytoplankton PIC plankton POC polar regions pollutants precipitation predation prediction primary production primary productivity Prochlorococcus proteins pteropods pycnocline radioisotopes remineralization remote sensing repeat hydrography residence time resource management respiration resuspension rivers rocky shore Rossby waves Ross Sea ROV salinity salt marsh satell satellite scale seafloor seagrass sea ice sea level rise seasonal patterns seasonal trends sea spray seaweed sediments sensors shelf system shells ship-based observations shorelines silicate sinking particles size SOCCOM soil carbon southern ocean south pacific spatial covariations speciation SST stoichiometry subduction submesoscale subpolar subtropical sulfate surf surface surface ocean Synechococcus teleconnections temperate temperature temporal covariations thermocline thermodynamics thermohaline thorium tidal time-series time of emergence top predators total alkalinity trace elements trace metals trait-based transfer efficiency transient features Tris trophic transfer tropical turbulence twilight zone upper ocean upper water column upwelling US CLIVAR validation velocity gradient ventilation vertical flux vertical migration vertical transport volcano warming water clarity water quality western boundary currents wetlands winter mixing world ocean compilation zooplankton

Copyright © 2022 - OCB Project Office, Woods Hole Oceanographic Institution, 266 Woods Hole Rd, MS #25, Woods Hole, MA 02543 USA Phone: 508-289-2838  •  Fax: 508-457-2193  •  Email: ocb_news@us-ocb.org

link to nsflink to noaalink to WHOI

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.