The circulation and transformations of Atlantic water in the Arctic Mediterranean Sea

AbstractBaffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.

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Early Holocene ocean conditions off the Zachariæ Isstrøm, Northeast Greenland

10.5194/egusphere-egu21-15076 ◽

2021 ◽

Author(s):

Joanna Davies ◽

Anders Møller Mathiasen ◽

Kristiane Kristensen ◽

Christof Pearce ◽

Marit-Solveig Seidenkrantz

Keyword(s):

Climate Change ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Atlantic Water ◽

The Arctic ◽

Future Climate Change ◽

Polar Regions ◽

Ice Shelf ◽

Outlet Glacier ◽

The Impact

The polar regions exhibit some of the most visible signs of climate change globally; annual mass loss from the Greenland Ice Sheet (GrIS) has quadrupled in recent decades, from 51 &#177; 65 Gt yr&#8722;1 (1992-2001) to 211 &#177; 37 Gt yr&#8722;1 (2002-2011). This can partly be attributed to the widespread retreat and speed-up of marine-terminating glaciers. The Zachariae Isstr&#248;m (ZI) is an outlet glacier of the Northeast Greenland Ice Steam (NEGIS), one of the largest ice streams of the GrIS (700km), draining approximately 12% of the ice sheet interior. Observations show that the ZI began accelerating in 2000, resulting in the collapse of the floating ice shelf between 2002 and 2003. By 2014, the ice shelf extended over an area of 52km2, a 95% decrease in area since 2002, where it extended over 1040km2. Paleo-reconstructions provide an opportunity to extend observational records in order to understand the oceanic and climatic processes governing the position of the grounding zone of marine terminating glaciers and the extent of floating ice shelves. Such datasets are thus necessary if we are to constrain the impact of future climate change projections on the Arctic cryosphere.A multi-proxy approach, involving grain size, geochemical, foraminiferal and sedimentary analysis was applied to marine sediment core DA17-NG-ST8-92G, collected offshore of the ZI, on &#160;the Northeast Greenland Shelf. The aim was to reconstruct changes in the extent of the ZI and the palaeoceanographic conditions throughout the Early to Mid Holocene (c.a. 12,500-5,000 cal. yrs. BP). Evidence from the analysis of these datasets indicates that whilst there has been no grounded ice at the site over the last 12,500 years, the ice shelf of the ZI extended as a floating ice shelf over the site between 12,500 and 9,200 cal. yrs. BP, with the grounding line further inland from our study site. This was followed by a retreat in the ice shelf extent during the Holocene Thermal Maximum; this was likely to have been governed, in part, by basal melting driven by Atlantic Water (AW) recirculated from Svalbard or from the Arctic Ocean. Evidence from benthic foraminifera suggest that there was a shift from the dominance of AW to Polar Water at around 7,500 cal. yrs. BP, although the ice shelf did not expand again despite of this cooling of subsurface waters.

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Propagation of Thermohaline Anomalies and their predictive potential in the Northern North Atlantic

10.5194/egusphere-egu21-15092 ◽

2021 ◽

Author(s):

Helene R. Langehaug ◽

Pablo Ortega ◽

Francois Counillon ◽

Daniela Matei ◽

Elizabeth Maroon ◽

...

Keyword(s):

Time Scales ◽

North Atlantic ◽

Atlantic Water ◽

The Arctic ◽

Lead Times ◽

Band Pass Filter ◽

Pass Filter ◽

Predictive Skill ◽

Prediction Systems ◽

Water Pathway

In this study we assess to what extent seven different dynamical prediction systems can retrospectively predict the winter sea surface temperature (SST) in the subpolar North Atlantic and the Nordic Seas in the time period 1970-2005. We focus in particular on the region where warm water flows poleward, i.e., the Atlantic water pathway, and on interannual-to-decadal time scales. To better understand why dynamical prediction systems have predictive skill or lack thereof, we confront them with a mechanism identified from observations &#8211; propagation of oceanic anomalies from low to high latitudes &#8211; on different forecast lead times. This observed mechanism shows that warm and cold anomalies propagate along the Atlantic water pathway within a certain time frame. A key result from this study is that most models have difficulty representing this mechanism, resulting in an overall poor prediction skill after 1-2 years lead times (after applying a band-pass filter to focus on interannual-to-decadal time scales). There is a link, although not very strong, between predictive skill and the representation of the SST propagation. Observational studies demonstrate predictability several years in advance in this region, thus suggesting a great potential for improvement of dynamical climate predictions by resolving the causes for the misrepresentation of the oceanic link. Inter model differences in simulating surface velocities along the Atlantic water pathway suggest that realistic velocities are important to better circulate anomalies poleward, and hence, increase predictive skill on interannual-to-decadal time scales in the oceanic gateway to the Arctic.

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Eastern Arctic Ocean Diapycnal Heat Fluxes through Large Double-Diffusive Steps

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0080.1 ◽

2019 ◽

Vol 49 (1) ◽

pp. 227-246 ◽

Cited By ~ 5

Author(s):

Igor V. Polyakov ◽

Laurie Padman ◽

Y.-D. Lenn ◽

Andrey Pnyushkov ◽

Robert Rember ◽

...

Keyword(s):

Arctic Ocean ◽

Dissipation Rate ◽

Critical Role ◽

Density Ratio ◽

Atlantic Water ◽

Heat Fluxes ◽

The Arctic ◽

Eurasian Basin ◽

Average Flux ◽

Double Diffusive

AbstractThe diffusive layering (DL) form of double-diffusive convection cools the Atlantic Water (AW) as it circulates around the Arctic Ocean. Large DL steps, with heights of homogeneous layers often greater than 10 m, have been found above the AW core in the Eurasian Basin (EB) of the eastern Arctic. Within these DL staircases, heat and salt fluxes are determined by the mechanisms for vertical transport through the high-gradient regions (HGRs) between the homogeneous layers. These HGRs can be thick (up to 5 m and more) and are frequently complex, being composed of multiple small steps or continuous stratification. Microstructure data collected in the EB in 2007 and 2008 are used to estimate heat fluxes through large steps in three ways: using the measured dissipation rate in the large homogeneous layers; utilizing empirical flux laws based on the density ratio and temperature step across HGRs after scaling to account for the presence of multiple small DL interfaces within each HGR; and averaging estimates of heat fluxes computed separately for individual small interfaces (as laminar conductive fluxes), small convective layers (via dissipation rates within small DL layers), and turbulent patches (using dissipation rate and buoyancy) within each HGR. Diapycnal heat fluxes through HGRs evaluated by each method agree with each other and range from ~2 to ~8 W m−2, with an average flux of ~3–4 W m−2. These large fluxes confirm a critical role for the DL instability in cooling and thickening the AW layer as it circulates around the eastern Arctic Ocean.

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The use of Cs and Sr isotopes as tracers in the Arctic Mediterranean Seas

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1988.0049 ◽

1988 ◽

Vol 325 (1583) ◽

pp. 161-176 ◽

Cited By ~ 36

Keyword(s):

Deep Water ◽

Thermohaline Circulation ◽

Atlantic Water ◽

The Arctic ◽

Coastal Current ◽

Intermediate Water ◽

Sr Isotopes ◽

Arctic Ice ◽

Norwegian Coastal Current

The Arctic Mediterranean Seas constitute an oceanic region in which the thermohaline circulation has a strong advective component and deep ventilation processes are very active relative to other oceanic areas. Details of the nature of these circulation and ventilation processes have been revealed through use of Cs and Sr isotopes from bomb-fallout and nuclear-waste sources as ocean tracers. In both cases, their regional input is dominated by advective supply in the Norwegian Atlantic Current and Norwegian Coastal Current, respectively. The different temporal, spatial, and compositional input patterns of these tracers have been used to study different facets of the regional circulation. These input differences and some representative applications of the use of these tracers are reviewed. The data discussed derive from samples collected both from research vessels and from Arctic ice camps. The topics addressed include: ( a ) the role of Arctic Intermediate Water as source, supplying recent surface water to North Atlantic Deep Water via the Denmark Strait overflow; ( b ) deep convective mixing in the Greenland Sea; ( c ) circulation or recirculation of Atlantic water in the Arctic basins; and ( d ) the role of Arctic shelfwaters in the ventilation of intermediate and deep water in the Eurasian and Canadian basins.

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Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean

Journal of Climate ◽

10.1175/jcli-d-19-0976.1 ◽

2020 ◽

Vol 33 (18) ◽

pp. 8107-8123 ◽

Cited By ~ 6

Author(s):

Igor V. Polyakov ◽

Tom P. Rippeth ◽

Ilker Fer ◽

Matthew B. Alkire ◽

Till M. Baumann ◽

...

Keyword(s):

Heat Flux ◽

Sea Ice ◽

Arctic Ocean ◽

Mixed Layer ◽

Winter Season ◽

Atlantic Water ◽

The Arctic ◽

Surface Mixed Layer ◽

Winter Convection ◽

Oceanic Heat Flux

AbstractA 15-yr duration record of mooring observations from the eastern (>70°E) Eurasian Basin (EB) of the Arctic Ocean is used to show and quantify the recently increased oceanic heat flux from intermediate-depth (~150–900 m) warm Atlantic Water (AW) to the surface mixed layer and sea ice. The upward release of AW heat is regulated by the stability of the overlying halocline, which we show has weakened substantially in recent years. Shoaling of the AW has also contributed, with observations in winter 2017–18 showing AW at only 80 m depth, just below the wintertime surface mixed layer, the shallowest in our mooring records. The weakening of the halocline for several months at this time implies that AW heat was linked to winter convection associated with brine rejection during sea ice formation. This resulted in a substantial increase of upward oceanic heat flux during the winter season, from an average of 3–4 W m−2 in 2007–08 to >10 W m−2 in 2016–18. This seasonal AW heat loss in the eastern EB is equivalent to a more than a twofold reduction of winter ice growth. These changes imply a positive feedback as reduced sea ice cover permits increased mixing, augmenting the summer-dominated ice-albedo feedback.

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Characterization of the Atlantic Water and Levantine Intermediate Water in the Mediterranean Sea using Argo Float Data

10.5194/os-2021-68 ◽

2021 ◽

Author(s):

Giusy Fedele ◽

Elena Mauri ◽

Giulio Notarstefano ◽

Pierre Marie Poulain

Keyword(s):

Mediterranean Sea ◽

Thermohaline Circulation ◽

Internal Variability ◽

Warming Trend ◽

Atlantic Water ◽

Western Mediterranean ◽

Water Masses ◽

Intermediate Water ◽

Starting Point ◽

The Mediterranean

Abstract. The Atlantic Water (AW) and Levantine Intermediate Water (LIW) are important water masses that play a crucial role in the internal variability of the Mediterranean thermohaline circulation. In particular, their variability and interaction, along with other water masses that characterize the Mediterranean basin, such as the Western Mediterranean Deep Water (WMDW), contribute to modify the Mediterranean Outflow through the Gibraltar Strait and hence may influence the stability of the global thermohaline circulation. This work aims to characterize the AW and LIW in the Mediterranean Sea, taking advantage of the large observational dataset provided by Argo floats from 2001 to 2019. Using different diagnostics, the AW and LIW were identified, highlighting the inter-basin variability and the strong zonal gradient that characterize the two water masses in this marginal sea. Their temporal variability was also investigated focusing on trends and spectral features which constitute an important starting point to understand the mechanisms that are behind their variability. A clear salinification and warming trend have characterized the AW and LIW in the last two decades (~0.007 and 0.008 yr−1; 0.018 and 0.007 °C yr−1, respectively). The salinity and temperature trends found at subbasin scale are in good agreement with previous results. The strongest trends are found in the Adriatic basin in both the AW and LIW properties. A subbasin dependent spectral variability emerges in the AW and LIW salinity timeseries with peaks between 2 and 10 years.

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Background Levels of Dissolved/Dispersed Petroleum Residues in the Gulf of St. Lawrence, 1970–79

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f85-072 ◽

1985 ◽

Vol 42 (3) ◽

pp. 544-555 ◽

Cited By ~ 8

Author(s):

E. M. Levy

Keyword(s):

Atmospheric Deposition ◽

East Coast ◽

Atlantic Water ◽

Point Sources ◽

The Arctic ◽

Present Level ◽

Background Levels ◽

Petroleum Residues ◽

Substantial Decline

A 10-yr program of monitoring the incidence and distribution of dissolved/dispersed petroleum residues in the Gulf of St. Lawrence confirmed that the major source is the Atlantic water that enters through Cabot Strait and demonstrated that a substantial decline in the background levels occurred during the mid-1970's. The present level, about 0.4 μg/L, is similar to those of other unpolluted areas off the east coast of Canada and in the Arctic where it appears that the input from atmospheric deposition exceeds those from accidental spills, deliberate discharges, and other point sources.

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The role of sea ice for plastic pollution in the Arctic

10.5194/egusphere-egu21-13366 ◽

2021 ◽

Author(s):

Ilka Peeken ◽

Elisa Bergami ◽

Ilaria Corsi ◽

Benedikt Hufnagl ◽

Christian Katlein ◽

...

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Long Range ◽

Environmental Concern ◽

Ice Cores ◽

Atlantic Water ◽

The Arctic ◽

Polar Regions ◽

Plastic Pollution ◽

The Arctic Ocean

Marine plastic pollution is a growing worldwide environmental concern as recent reports indicate that increasing quantities of litter disperse into secluded environments, including Polar Regions. Plastic degrades into smaller fragments under the influence of sunlight, temperature changes, mechanic abrasion and wave action resulting in small particles < 5mm called microplastics (MP). Sea ice cores, collected in the Arctic Ocean have so far revealed extremely high concentrations of very small microplastic particles, which might be transferred in the ecosystem with so far unknown consequences for the ice dependant marine food chain.&#160; Sea ice has long been recognised as a transport vehicle for any contaminates entering the Arctic Ocean from various long range and local sources. The Fram Strait is hereby both, a major inflow gateway of warm Atlantic water, with any anthropogenic imprints and the major outflow region of sea ice originating from the Siberian shelves and carried via the Transpolar Drift. The studied sea ice revealed a unique footprint of microplastic pollution, which were related to different water masses and indicating different source regions. Climate change in the Arctic include loss of sea ice, therefore, large fractions of the embedded plastic particles might be released and have an impact on living systems. By combining modeling of sea ice origin and growth, MP particle trajectories in the water column as well as MPs long-range transport via particle tracking and transport models we get first insights &#160;about the sources and pathways of MP in the Arctic Ocean and beyond and how this might affect the Arctic ecosystem.

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