Kumiko Azetsu-Scott

Oxygen isotope studies from Iceland to an East Greenland Fjord: behaviour of glacial meltwater plume

Abstract A detailed study of the oxygen isotope composition (δ18O) was carried out along a transect between Iceland and East Greenland, which includes the West Iceland Shelf, Denmark Strait, the Kangerdlugssuaq Trough on the East Greenland Shelf and the Kangerdlugssuaq Fjord. Vertical profiles of the oxygen isotope composition in a fjord with tidewater glaciers were studied for the first time. In this study, three distinct water masses are identified from oxygen isotope measurements: (1) North Atlantic Water of δ18O ≈ 0%. occupies the Icelandic Shelf, Denmark Strait subsurface, and deep waters of the Kangerdlugssuaq Trough and Fjord; (2) the East Greenland Current of δ18O ≈ −2%. occupies surface water at the western Denmark Strait and the Kangerdlugssuaq Trough; (3) glacial meltwater (δ18O ranges from −30 to −20%. in source) flows at the surface of the Kangerdlugssuaq Fjord. Surface δ18O data distinctively identify the East Greenland Front between North Atlantic Water and the East Greenland Current in Denmark Strait. Vertical profiles of δ18O show the steady increase from surface to deep water at the stations west of the front with well mixed water at stations east of the front. We did not find any subsurface glacial meltwater intrusion in Kangerdlugssuaq fjord, unlike the reported ‘cold tongue’ in Antarctic fjords. Instead Arctic Intermediate Water (winter cooled North Atlantic Water) penetrates to the head of the fjord and fills the bottom part of the fjord. A linear relationship between salinity and δ18O shows that there was no significant contribution from the sea ice meltwater in this study site. The dominant source of freshwater in the Kangerdlugssuaq Fjord is glacial meltwater. A simple model using δ18O was developed to illustrate glacial meltwater dynamics in the fjord, and to estimate the length of the glacial meltwater plume. Model results agree well with the data within the fjord and near the fjord mouth and a plume length is estimated to be 250 km from the glacial face. However, a diversion of the model from the data is observed at about 70 km away from the mouth of the fjord because of the influence by the East Greenland Current and the Coriolis effect.

Baseline Monitoring of the Western Arctic Ocean Estimates 20% of Canadian Basin Surface Waters Are Undersaturated with Respect to Aragonite

Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index) for the western Arctic Ocean. This data set documents aragonite undersaturation in ∼20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean’s largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater.

Skeletal Mg/Ca in Primnoa resedaeformis: relationship to temperature?

It has been suggested that the deep-sea gorgonian coral Primnoa resedaeformis may be an important paleoceanographic archive. Seventeen colonies collected from the upper slope of the NW Atlantic margin (229 – 447 m) were analyzed to see if skeletal Mg/Ca is related to temperature. Analyses were focused on the calcite cortex region of skeletal sections to avoid interference from organic Mg in the horny layers found closer to the center of sections. Comparison of bulk skeletal Mg/Ca with hydrographic temperature yielded the relationship Mg/Ca (mmol/mol)=5 (+/− 1.4) T (°C)+64 (+/− 10). This relationship was used to calibrate profiles of Mg/Ca measured across the annual rings of one large, well-dated colony, over the period 1950–2002. Mg/Ca profiles were broadly consistent among three sections spaced 10 cm apart along the main trunk of the colony. These profiles were in general agreement with the local instrumental record of temperature at 375 – 450 m. Some discrepancies between the coral and instrumental records of temperature may be a result of chronological error, poor sampling density, or additional factors influencing Mg partitioning in the coral. Overall, these preliminary results support the hypothesis that temperature drives Mg/Ca in the skeletal calcite of this species. It appears that environmentally meaningful records from Primnoa resedaeformis will be found at decadal scales or longer.

Influence of melting icebergs on distribution, characteristics and transport of marine particles in an East Greenland fjord

A detailed study of distribution of suspended sediments in an East Greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers (INLs). Observed INLs extended from the head to the mouth of the fjord at water depths between 100 and 400 m. Particulate organic carbon and nitrogen, chlorophyll a, and nutrient measurements and observation by microscope and energy dispersive X-ray analyses were used to characterize marine particles. Particles in the INLs are composed of glacial flour including >50 μm quartz and feldspar grains with angular and sharp edges, considered to be released from melting icebergs. In situ photographs show large aggregates (>1 mm) at high concentration (>300 particles per liter) in and below INLs. These aggregates, in comparison with the dispersed particle size distribution, demonstrate that smaller size particles (e.g., clay) settle effectively along with larger single size grains. In Kangerlugssuaq Fjord, the mass transport of marine particles was governed by the subsurface iceberg melting, producing observed INLs, rather than the surface meltwater plume. This suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water, as well as the spread of cold and fresh water in the surface layer, needs to be considered to evaluate the occurrence of ice-rafted debris layers, including Heinrich layers. This study provides the field evidence of a modern analogue on ocean conditions that could form iceberg-rafted layers.

Low calcium carbonate saturation state in an Arctic inland sea having large and varying fluvial inputs: The Hudson Bay system

The Hudson Bay system (HBS) is a shallow inland sea in the Arctic, composed of Hudson Strait, Foxe Basin/Channel, James Bay, and Hudson Bay. Dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements were used to investigate the state of ocean acidification, specifically calcium carbonate saturation states (Ω) and pH. The freshwater sources were identified from the relationship between oxygen isotope composition (δ18O) and salinity to understand the role of freshwater in ocean acidification. The saturation state of seawater with respect to calcium carbonate (Ω) in surface water ( 10%). The watershed characteristics, however, influenced the alkalinity of river runoff in different parts of Hudson Bay, which contributed to Ω variation in the coastal region. In southwestern Hudson Bay where the watershed is dominated by limestone, Ω was higher compared to eastern Hudson Bay, where the watershed consists of an igneous rock formation. In deeper waters, low Ω is caused by remineralization of organic matter. The highest DIC concentrations (>2300 µmol/kg) were observed in the depths of central Hudson Bay with a pHtotal of 7.49 and Ωarg of 0.37. Over 67% and 22% of the bottom water of Hudson Bay was undersaturated with respect to aragonite and calcite respectively, despite Hudson Bay being very shallow (less than 250 m deep). The aragonite saturation horizon in the central Hudson Bay was around 50 m.

Time series measurements of transient tracers and tracer derived transport in the deep western boundary current between the Labrador Sea and the subtropical Atlantic Ocean at Line W

Time series measurements of the nuclear fuel reprocessing tracer, 129I and the gas ventilation tracer, CFC-11 were undertaken on the AR7W section in the Labrador Sea (1997-2014) and on Line W (2004-2014), located over the US continental slope off Cape Cod, to determine advection and mixing time scales for the transport of Denmark Strait Overflow Water (DSOW) within the Deep Western Boundary Current (DWBC). Tracer measurements were also conducted in 2010 over the continental rise southeast of Bermuda to intercept the equator-ward flow of DSOW by interior pathways. The Labrador Sea tracer and hydrographic time series data were used as input functions in a boundary current model that employs transit time distributions to simulate the effects of mixing and advection on downstream tracer distributions. Model simulations of tracer levels in the boundary current core and adjacent interior (shoulder) region with which mixing occurs were compared with the Line W time series measurements to determine boundary current model parameters. These results indicate that DSOW is transported from the Labrador Sea to Line W via the DWBC on a time scale of 5-6 y corresponding to a mean flow velocity of 2.7 cm/s while mixing between the core and interior regions occurs with a time constant of 2.6 y. A tracer section over the southern flank of the Bermuda rise indicates that the flow of DSOW that separated from the DWBC had undergone transport through interior pathways on a time scale of 9 y with a mixing time constant of 4 y. This article is protected by copyright. All rights reserved.

The subpolar gyre regulates silicate concentrations in the North Atlantic

The North Atlantic is characterized by diatom-dominated spring blooms that results in significant transfer of carbon to higher trophic levels and the deep ocean. These blooms are terminated by limiting silicate concentrations in summer. Numerous regional studies have demonstrated phytoplankton community shifts to lightly-silicified diatoms and non-silicifying plankton at the onset of silicate limitation. However, to understand basin-scale patterns in ecosystem and climate dynamics, nutrient inventories must be examined over sufficient temporal and spatial scales. Here we show, from a new comprehensive compilation of data from the subpolar Atlantic Ocean, clear evidence of a marked pre-bloom silicate decline of 1.5–2 µM throughout the winter mixed layer during the last 25 years. This silicate decrease is primarily attributed to natural multi-decadal variability through decreased winter convection depths since the mid-1990s, a weakening and retraction of the subpolar gyre and an associated increased influence of nutrient-poor water of subtropical origin. Reduced Arctic silicate import and the projected hemispheric-scale climate change-induced weakening of vertical mixing may have acted to amplify the recent decline. These marked fluctuations in pre-bloom silicate inventories will likely have important consequences for the spatial and temporal extent of diatom blooms, thus impacting ecosystem productivity and ocean-atmosphere climate dynamics.

Energy metabolism and survival of the juvenile recruits of the American lobster (Homarus americanus) exposed to a gradient of elevated seawater pCO2

The transition from the last pelagic larval stage to the first benthic juvenile stage in the complex life cycle of marine invertebrates, such as the American lobster Homarus americanus, a species of high economic importance, represents a delicate phase in these species development. Under future elevated pCO2 conditions, ocean acidification and other elevated pCO2 events can negatively affect crustaceans. This said their effects on the benthic settlement phase are virtually unknown. This study aimed to identify the effects of elevated seawater pCO2 on stage V American lobsters exposed to seven pCO2 levels. The survival, development time, metabolic and feeding rates, carapace composition, and energy metabolism enzyme function were investigated. Results suggested an increase in mortality, slower development and an increase in aerobic capacity with increasing pCO2. Our study points to potential reduction in juvenile recruitment success as seawater pCO2 increases, thus foreshadowing important socio-economic repercussions for the lobster fisheries and industry.

Using natural analogues to investigate the effects of climate change and ocean acidification on Northern ecosystems

Samuel S. P. Rastrick*, Helen Graham, Kumiko Azetsu-Scott, Piero Calosi, Melissa Chierici, Agneta Fransson, Haakon Hop, Jason Hall-Spencer, Marco Milazzo, Peter Thor, and Tina Kutti Institute of Marine Research, PO Box 1870 Nordnes, 5870 Bergen, Norway Ocean Bergen, Espelandvegen 232, Blomsterdalen, Norway Department of Fisheries and Oceans, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada Département de Biologie, Chimie et Géographie, Université du Quebéc à Rimouski, 300 Allée des Ursulines, Rimouski, QC G5L 3A1, Canada Institute of Marine Research, Fram Centre, 9007 Tromsø, Norway University Centre in Svalbard, Longyearbyen, Norway Norwegian Polar Institute, Fram Centre, N-9296 Tromsø, Norway Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, UiT The Arctic University of Norway, N-9037 Tromsø, Norway Marine Biology and Ecology Research Centre, School of Marine Science and Engineering, Plymouth University, Drake Circus, Plymouth, Devon PL4 8AA, UK Department of Earth and Marine Science, Università degli studi di Palermo, CoNISMa, Via Archirafi 20, I-90123 Palermo, Italy *Corresponding author: tel: þ4747489401; e-mail: samuel.rastrick@imr.no.

Cascading off the West Greenland Shelf: A numerical perspective

Cascading of dense water from the shelf to deeper layers of the adjacent ocean basin has been observed in several locations around the world. The West Greenland Shelf (WGS), however, is a region where this process has never been documented. In this study, we use a numerical model with a 1/4° resolution to determine (i) if cascading could happen from the WGS; (ii) where and when it could take place; (iii) the forcings that induce or halt this process; and (iv) the path of the dense plume. Results show cascading happening off the WGS at Davis Strait. Dense waters form there due to brine rejection and slide down the slope during spring. Once the dense plume leaves the shelf, it gradually mixes with waters of similar density and moves northward into Baffin Bay. Our simulation showed events happening between 2003-2006 and during 2014; but no plume was observed in the simulation between 2007-2013. We suggest that the reason why cascading was halted in this period is related to: the increased freshwater transport from the Arctic Ocean through Fram Strait; the additional sea ice melting in the region; and the reduced presence of Irminger Water at Davis Strait during fall/early winter. Although observations at Davis Strait show that our simulation usually overestimates the seasonal range of temperature and salinity, they agree with the overall variability captured by the model. This suggests that cascades have the potential to develop on the WGS, albeit less dense than the ones estimated by the simulation.