Oceans Melting Greenland: Early Results from NASA's Ocean-Ice Mission in Greenland

Melting of the Greenland Ice Sheet represents a major uncertainty in projecting future rates of global sea level rise. Much of this uncertainty is related to a lack of knowledge about subsurface ocean hydrographic properties, particularly heat content, how these properties are modified across the continental shelf, and about the extent to which the ocean interacts with glaciers. Early results from NASA’s five-year Oceans Melting Greenland (OMG) mission, based on extensive hydrographic and bathymetric surveys, suggest that many glaciers terminate in deep water and are hence vulnerable to increased melting due to ocean-ice interaction. OMG will track ocean conditions and ice loss at glaciers around Greenland through the year 2020, providing critical information about ocean-driven Greenland ice mass loss in a warming climate

Bathymetry of Southeast Greenland From Oceans Melting Greenland (OMG) Data

Southeast Greenland has been a major participant in the ice sheet mass loss over the last several decades. Interpreting the evolution of glacier fronts requires information about their depth below sea level and ocean thermal forcing, which are incompletely known in the region. Here, we combine airborne gravity and multibeam echo sounding data from the National Aeronautics and Space Administration's Oceans Melting Greenland (OMG) mission with ocean probe and fishing boat depth data to reconstruct the bathymetry extending from the glacier margins to the edges of the continental shelf. We perform a three‐dimensional inversion of the gravity data over water and merge the solution with a mass conservation reconstruction of bed topography over land. In contrast with other parts of Greenland, we find few deep troughs connecting the glaciers to the sources of warm Atlantic Water, amidst a relatively uniform, shallow (350 m) continental shelf. The deep channels include the Kangerlugssuaq, Sermilik, Gyldenløve, and Tingmiarmiut Troughs

Identifying Spatial Variability in Greenland’s Outlet Glacier Response to Ocean Heat

Although the Greenland ice sheet is losing mass as a whole, patterns of change on both local and regional scales are complex. Spatial statistics reveal large spatial variability of dynamic thinning rates of Greenland’s marine-terminating glaciers between 2003 and 2009; only 18% of glacier thinning rates co-vary with neighboring glaciers. Most spatially-correlated thinning rates are clusters of stable glaciers in the Thule, Scoresby Sund, and Southwest regions. Conversely, where spatial-autocorrelation is low, individual glaciers are more strongly controlled by local, glacier-scale features than by regional influences. We investigate possible sources of local control of oceanic forcing by combining grounding line depths and ocean model output to estimate mean ocean heat content adjacent to 74 glaciers. Linear regression models indicate stronger correlation of dynamic thinning rates with ocean heat content compared to those with grounding line depths alone. The correlation between ocean heat and dynamic thinning is robust for all of Greenland except glaciers in the West, and strongest in the Southeast (R2 ∼ 0.81 ± 0.15, ρ = 0.009), implying that glaciers with deeper grounded termini here are most sensitive to changes in ocean forcing. In the Northwest, accounting for shallow sills in the regressions improves the correlation of water depth with glacial thinning, highlighting the need for comprehensive knowledge of fjord geometry

The International Bathymetric Chart of the Arctic Ocean Version 4.0

Funder: The Nippon Foundation of Japan, grant Seabed 2030Funder: Open access funding provided by Stockholm UniversityAbstract: Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet

Submarine Moraines in Southeast Greenland Fjords Reveal Contrasting Outlet-Glacier Behavior since the Last Glacial Maximum

Knowledge of the past behavior of the outlet glaciers of Southeast (SE) Greenland is necessary to understand and model spatial differences in the response of the Greenland Ice Sheet (GIS) to climatic changes. Here we use bathymetric data to map the distribution of more than 50 major moraines in SE Greenland fjords. Inner-fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords. We identify, for the first time, nine midfjord moraines that span the approximately 150-km-long eastern margin of the Julianehåb Ice Cap. In contrast, midfjord moraines are generally absent from the deeper and wider fjords of the SE GIS. The variable distribution of midfjord moraines along the SE Greenland margin reveals contrasting behavior of the SE GIS and the eastern Julianehåb Ice Cap during the last deglaciation, which probably reflects differences in fjord geometry and exposure to ocean heat

The feeding ecology and microbiome of the pteropod Limacina helicina antarctica

The pteropod (pelagic snail) Limacina helicina antarctica is a dominant grazer alongthe Western Antarctic Peninsula (WAP) and plays an important role in regional food web dynamics and biogeochemical cycling. For the first time, we examined the gut microbiome and feeding ecology of L. h. antarctica based on 16S and 18S rRNA gene sequences of gut contents in the WAP during austral summer. Eukaryotic gut contents of L. h. antarctica indicate that this species predominantly feeds on diatoms and dinoflagellates, supplementing its diet with ciliates and foraminifera. Mollicutes bacteria were a consistent component of the gut microbiome. Determining the gut microbiome and feeding ecology of L. h.antarctica aids in identifying the underlying mechanisms controlling pteropod abundance and distribution in a region of rapid environmental change

Role of habitat and predators in maintaining functional diversity of estuarine bivalves

Habitat loss is occurring rapidly in coastal systems worldwide. In Chesapeake Bay, USA, most historical oyster reefs have been decimated, and seagrass loss is expected to worsen due to climate warming and nutrient pollution. This loss of habitat may result in declining diversity, but whether diversity loss will equate to loss in ecosystem function is unknown. A bivalve survey was conducted in a variety of habitat types (seagrass, oyster shell, shell hash, coarse sand, detrital mud) in 3 lower Chesapeake Bay sub-estuaries from spring 2012 through summer 2013 to examine the correlation between bivalve densities, habitat type, habitat volume (of material retained on 3 mm mesh), and predator density. Bivalves were analyzed as functional groups based on feeding mode, living position, and predator defense strategy. On average, seagrass supported one additional functional group, and diversity was increased 68-94%, in seagrass compared to the other habitats examined. Species richness and functional group richness were positively correlated with habitat volume. The greatest densities of deposit-feeding bivalves were in detrital mud habitats, the greatest densities of thin-shelled and surface-dwelling bivalves were in seagrass habitats, and the greatest densities of armored bivalves were in oyster shell habitats. Small, thin-shelled bivalves were negatively correlated with densities of predators, including blue crabs Callinectes sapidus and cownose rays Rhinoptera bonasus. Overall, bivalve diversity was as - sociated with habitat type, habitat volume, and predator densities. These results suggest that all habitats, and particularly seagrass, play a role in maximizing bivalve functional diversity in Chesapeake Bay

Zooplankton diel vertical migration during Antarctic summer

Zooplankton diel vertical migration (DVM) during summer in the polar oceans is presumed to be dampened due to near continuous daylight. We analyzed zooplankton diel vertical distribution patterns in a wide range of taxa along the Western Antarctic Peninsula (WAP) to assess if DVM occurs, and if so, what environmental controls modulate DVM in the austral summer. Zooplankton were collected during January and February in paired day-night, depth-stratified tows through the mesopelagic zone along the WAP from 2009-2017, as well as in day and night epipelagic net tows from 1993-2017. The copepod Metridia gerlachei, salp Salpa thompsoni, pteropod Limacina helicina antarctica, and ostracods consistently conducted DVM between the mesopelagic and epipelagic zones. Migration distance for M. gerlachei and ostracods decreased as photoperiod increased from 17 to 22 h daylight. The copepods Calanoides acutus and Rhincalanus gigas, as well as euphausiids Thysanoessa macrura and Euphausia crystallorophias, conducted shallow (mostly within the epipelagic zone) DVMs into the upper 50 m at night. Rhincalanus gigas, T. macrura, and L. h. antarctica DVM behavior was modulated by chlorophyll a concentration, mixed layer depth, and depth of the subsurface chlorophyll a maximum, respectively. Carnivorous and detritivorous taxa – including the calanoid copepod Paraeuchaeta antarctica, ostracods, chaetognaths, and Tomopteris spp. polychaetes – as well as seasonally migrating copepods, were most abundant in the mesopelagic zone regardless of the diel cycle. Paraeuchaeta antarctica underwent reverse DVM within the top 100 m. The impacts of Antarctic zooplankton summer DVM and the resident mesopelagic assemblage on carbon export should be better quantified

Concentrations and uptake of neutral monosaccharides along 14°W in the equatorial Pacific: Contribution of glucose to heterotrophic bacterial activity and the DOM flux

We examined concentrations and uptake of dissolved neutral monosaccharides (DNMS) in order to determine the contribution of DNMS to heterotrophic bacterial production and to the flux of dissolved organic matler (DOM) in the equatorial Pacific. DNMS concentrations were greater during El Niño‐affected months of February–April 1992 than during August–October 1992; in contrast, glucose turnover was the opposite— turnover was faster in August–October than in February–April. The variation in sugar concentrations and turnover probably resulted from El Niño‐induced changes in primary production; as El Niño waned primary production increased, which appeared to stimulate bacterial activity, especially glucose turnover, that in turn forced down DNMS concentrations. In all months, however, DNMS concentrations were low, especially compared with total dissolved organic carbon concentrations (\u3c1%). Glucose was the dominant neutral monosaccharide and alone supported 15–47% of bacterial production. Other monosaccharides apparently did not support much bacterial growth; concentrations of other sugars were low, as probably was turnover. Respiration of glucose (30–60% of uptake) and mannose (60–90%) was relatively high, suggesting that DNMS supported a large fraction of bacterial respiration as well as biomass production. These results point to the importance of DNMS and glucose in particular in supporting bacterial growth and in contributing to the flux of labile DOM