Recent variability in the Atlantic water intrusion and water masses in Kongsfjorden, an Arctic fjord

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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Eemian Climatic and Hydrographical Instability on a Marine Shelf in Northern Denmark

Quaternary Research ◽

10.1006/qres.1996.1868 ◽

1997 ◽

Vol 47 (2) ◽

pp. 218-234 ◽

Cited By ~ 36

Author(s):

Marit-Solveig Seidenkrantz ◽

Karen Luise Knudsen

Keyword(s):

Ocean Circulation ◽

Atlantic Water ◽

Water Masses ◽

Last Interglacial ◽

Large Shift ◽

The North ◽

Oxygen Isotope Record ◽

Isotope Record ◽

First Millennium ◽

Holocene Record

Benthic foraminifera and stable isotope data from the last interglaciation (Eemian, substage 5e) from a borehole at Skagen, Denmark, provide evidence for major environmental and hydrographic changes during this period. During the first millennium of the Eemian, water masses covering northern Denmark became gradually warmer. Temperate conditions prevailed during most of the interglaciation, but these were interrupted by two periods with decreased water temperatures. The first cooling (Event S-1) was not very distinct at Skagen, but the second (Event S-2), seen in both the foraminiferal and oxygen isotope record, represents a large shift to subarctic conditions. Carbon isotopes indicate a change in ocean circulation during both events. No comparable climate variations are seen within the Holocene record at the site. The final cooling of the water masses associated with the substage 5e/5d boundary occurred within a few hundred years. These last interglacial climatic changes were probably caused by variations in strength and/or position of the North Atlantic Drift, possibly as a result of varying vigor of the Atlantic conveyor. In addition, minor variations in the fossil assemblages also indicate fluctuations in the inflow of Atlantic water to the Skagerrak–Kattegat area during the warm intervals of substage 5e.

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Comparison of water mass changes in the deep tropical Atlantic derived from Cd/Ca and carbon isotope records: Implications for changing Ba composition of Deep Atlantic Water Masses

Paleoceanography ◽

10.1029/98pa02670 ◽

1998 ◽

Vol 13 (6) ◽

pp. 572-585 ◽

Cited By ~ 27

Author(s):

Pamela A. Martin ◽

David W. Lea

Keyword(s):

Carbon Isotope ◽

Water Mass ◽

Atlantic Water ◽

Water Masses ◽

Tropical Atlantic

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Declining silicate concentrations in the Norwegian and Barents Seas

ICES Journal of Marine Science ◽

10.1093/icesjms/fss007 ◽

2012 ◽

Vol 69 (2) ◽

pp. 208-212 ◽

Cited By ~ 22

Author(s):

Francisco Rey

Keyword(s):

North Atlantic ◽

Relative Proportion ◽

Atlantic Water ◽

Water Masses ◽

Source Water ◽

Marine Science ◽

Norwegian Sea

Abstract Rey, F. 2012. Declining silicate concentrations in the Norwegian and Barents Seas. – ICES Journal of Marine Science, 69: 208–212. Since 1990, a decline in silicate concentrations together with increasing salinities has been observed in the Atlantic water of the Norwegian and Barents Seas. This decline in silicate has been found to be related to the relative proportion in which eastern and western source water masses from the northeastern North Atlantic enter the Norwegian Sea.

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Paleoenvironments along the Eastern Laurentide Ice Sheet Margin and Timing of the Last Ice Maximum and Retreat

Géographie physique et Quaternaire ◽

10.7202/032682ar ◽

2008 ◽

Vol 41 (2) ◽

pp. 265-277 ◽

Cited By ~ 18

Author(s):

Anne de Vernal ◽

Claude Hillaire-Marcel

Keyword(s):

Late Pleistocene ◽

North Atlantic ◽

Environmental Changes ◽

Atlantic Water ◽

Polar Front ◽

Water Masses ◽

Labrador Sea ◽

Eastern Canada ◽

North Atlantic Water ◽

Late Wisconsinan

ABSTRACT Palynological and isotopic analysis in a few deep-sea cores from the Labrador Sea reveals strong environmental changes related to the Late Pleistocene glacial fluctuations over eastern Canada. On the whole, the Labrador Sea was characterized by strong exchanges between North Atlantic water masses, Arctic outflows, and meltwater discharges from Laurentide, Greenland and lnuitian ice sheets. The penetration of temperate Atlantic waters persisted throughout most of the Late Pleistocene, with a brief interruption during the Late Wisconsinan. During this glacial substage, a slight but continuous meltwater runoff from the Laurentide ice margins grounded on the northern Labrador Shelf is indicated by relatively low 18O values and low-salinity (< 30‰) dinocyst assemblages. The calving of the ice margin, the melwater outflow and the subsequent dilution of surface waters offshore Labrador probably contributed to the dispersal of floating ice and, consequently, to a southward displacement of the polar front restraining the penetration of North Atlantic waters into the Labrador Sea. The advection of southern air masses along the Laurentide ice margins, shown by pollen assemblages, was favourable to abundant precipitation and therefore, high ice accumulation rates, especially over northern Labrador during the Late Wisconsinan. The déglaciation is marked by a brief, but significant, melting event of northern Laurentide ice shortly after 17 ka. The main glacial retreat occurred after ca. 11 ka. It allowed restoration of WSW-ENE atmospheric trajectories, increased phytoplanktonic productivity, and penetration of North Atlantic water masses into the Labrador Sea.

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Influence of Atlantic inflow on the freshwater content in the upper layer of the Arctic basin

Arctic and Antarctic Research ◽

10.30758/0555-2648-2019-65-4-363-388 ◽

2019 ◽

Vol 65 (4) ◽

pp. 363-388

Author(s):

G. V. Alekseev ◽

A. V. Pnyushkov ◽

A. V. Smirnov ◽

A. E. Vyazilova ◽

N. I. Glok

Keyword(s):

Fresh Water ◽

Large Scale ◽

Barents Sea ◽

Lower Boundary ◽

Arctic Basin ◽

Water Layer ◽

Atlantic Water ◽

Water Masses ◽

The Arctic ◽

The North

Inter-decadal changes in the water layer of Atlantic origin and freshwater content (FWC) in the upper 100 m layer were traced jointly to assess the influence of inflows from the Atlantic on FWC changes based on oceanographic observations in the Arctic Basin for the 1960s – 2010s. For this assessment, we used oceanographic data collected at the Arctic and Antarctic Research Institute (AARI) and the International Arctic Research Center (IARC). The AARI data for the decades of 1960s – 1990s were obtained mainly at the North Pole drifting ice camps, in high-latitude aerial surveys in the 1970s, as well as in ship-based expeditions in the 1990s. The IARC database contains oceanographic measurements acquired using modern CTD (Conductivity – Temperature – Depth) systems starting from the 2000s. For the reconstruction of decadal fields of the depths of the upper and lower 0 °С isotherms and FWC in the 0–100 m layer in the periods with a relatively small number of observations (1970s – 1990s), we used a climatic regression method based on the conservativeness of the large-scale structure of water masses in the Arctic Basin. Decadal fields with higher data coverage were built using the DIVAnd algorithm. Both methods showed almost identical results when compared. The results demonstrated that the upper boundary of the Atlantic water (AW) layer, identified with the depth of zero isotherm, raised everywhere by several tens of meters in 1990s – 2010s, when compared to its position before the start of warming in the 1970s. The lower boundary of the AW layer, also determined by the depth of zero isotherm, became deeper. Such displacements of the layer boundaries indicate an increase in the volume of water in the Arctic Basin coming not only through the Fram Strait, but also through the Barents Sea. As a result, the balance of water masses was disturbed and its restoration had to occur due to the reduction of the volume of the upper most dynamic freshened layer. Accordingly, the content of fresh water in this layer should decrease. Our results confirmed that FWC in the 0–100 m layer has decreased to 2 m in the Eurasian part of the Arctic Basin to the west of 180° E in the 1990s. In contrast, the FWC to the east of 180° E and closer to the shores of Alaska and the Canadian archipelago has increased. These opposite tendencies have been intensified in the 2000s and the 2010s. A spatial correlation between distributions of the FWC and the positions of the upper AW boundary over different decades confirms a close relationship between both distributions. The influence of fresh water inflow is manifested as an increase in water storage in the Canadian Basin and the Beaufort Gyre in the 1990s – 2010s. The response of water temperature changes from the tropical Atlantic to the Arctic Basin was traced, suggesting not only the influence of SST at low latitudes on changes in FWC, but indicating the distant tropical impact on Arctic processes.

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Enhancement of the North Atlantic CO<sub>2</sub> sink by Arctic Waters

Biogeosciences ◽

10.5194/bg-18-1689-2021 ◽

2021 ◽

Vol 18 (5) ◽

pp. 1689-1701

Author(s):

Jon Olafsson ◽

Solveig R. Olafsdottir ◽

Taro Takahashi ◽

Magnus Danielsen ◽

Thorarinn S. Arnarson

Keyword(s):

North Atlantic ◽

Thermohaline Circulation ◽

Atlantic Water ◽

Water Masses ◽

The Arctic ◽

Arctic Water ◽

The North ◽

The North Atlantic ◽

Co2 Sink ◽

The One

Abstract. The North Atlantic north of 50∘ N is one of the most intense ocean sink areas for atmospheric CO2 considering the flux per unit area, 0.27 Pg-C yr−1, equivalent to −2.5 mol C m−2 yr−1. The northwest Atlantic Ocean is a region with high anthropogenic carbon inventories. This is on account of processes which sustain CO2 air–sea fluxes, in particular strong seasonal winds, ocean heat loss, deep convective mixing, and CO2 drawdown by primary production. The region is in the northern limb of the global thermohaline circulation, a path for the long-term deep-sea sequestration of carbon dioxide. The surface water masses in the North Atlantic are of contrasting origins and character, with the northward-flowing North Atlantic Drift, a Gulf Stream offspring, on the one hand and on the other hand the cold southward-moving low-salinity Polar and Arctic waters with signatures from Arctic freshwater sources. We have studied by observation the CO2 air–sea flux of the relevant water masses in the vicinity of Iceland in all seasons and in different years. Here we show that the highest ocean CO2 influx is to the Arctic and Polar waters, respectively, -3.8±0.4 and -4.4±0.3 mol C m−2 yr−1. These waters are CO2 undersaturated in all seasons. The Atlantic Water is a weak or neutral sink, near CO2 saturation, after poleward drift from subtropical latitudes. These characteristics of the three water masses are confirmed by data from observations covering 30 years. We relate the Polar Water and Arctic Water persistent undersaturation and CO2 influx to the excess alkalinity derived from Arctic sources. Carbonate chemistry equilibrium calculations clearly indicate that the excess alkalinity may support at least 0.058 Pg-C yr−1, a significant portion of the North Atlantic CO2 sink. The Arctic contribution to the North Atlantic CO2 sink which we reveal was previously unrecognized. However, we point out that there are gaps and conflicts in the knowledge about the Arctic alkalinity and carbonate budgets and that future trends in the North Atlantic CO2 sink are connected to developments in the rapidly warming and changing Arctic. The results we present need to be taken into consideration for the following question: will the North Atlantic continue to absorb CO2 in the future as it has in the past?

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Spatial heterogeneity of Pelagia noctiluca ephyrae linked to water masses in the Western Mediterranean

PLoS ONE ◽

10.1371/journal.pone.0249756 ◽

2021 ◽

Vol 16 (4) ◽

pp. e0249756

Author(s):

Marina Pastor-Prieto ◽

Nixon Bahamon ◽

Ana Sabatés ◽

Antonio Canepa ◽

Josep-Maria Gili ◽

...

Keyword(s):

Latitudinal Gradient ◽

Atlantic Water ◽

Western Mediterranean ◽

Horizontal Distribution ◽

Population Connectivity ◽

Water Masses ◽

Strait Of Gibraltar ◽

Pelagia Noctiluca ◽

Diel Vertical Migrations ◽

The Mediterranean

Pelagia noctiluca is the most common jellyfish in the Western Mediterranean Sea, living in oceanic waters with a holoplanktonic lifecycle. Frequent outbreaks have been well documented in coastal areas, yet little is known about their offshore distribution. In this study we address the relationship between oceanographic structures and the distribution of P. noctiluca ephyrae along the central continental slope of the Western Mediterranean, covering a wide latitudinal gradient, during July-August 2016. The region is characterized by a rich and complex mesoscale surface circulation driven by the inflow of Atlantic Water into the Western Mediterranean through the Strait of Gibraltar. The results revealed a high variability in the ephyrae spatial paterns related with different water masses and the resulting mesoscale hydrographic features. Their horizontal distribution showed a clear latitudinal gradient with high abundances in the south, associated with recent Atlantic Water, and low abundances or absence in the north, in coincidence with the old Atlantic Water transported by the Northern Current. Ephyrae showed diel vertical migrations of short-extent in the first 50 m, with a wide distribution above the thermocline and the Deep Chlorophyll Maximum during daytime, being more concentrated towards the surface at night. The results suggest the population connectivity of P. noctiluca between the Atlantic and the Mediterranean. In that case, the abundance variability of the species in the Mediterranean could be modulated by its entrance associated with the inflow of Atlantic Water through the Strait of Gibraltar.

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Export of ice sheet meltwater from Upernavik Fjord, West Greenland

Journal of Physical Oceanography ◽

10.1175/jpo-d-21-0084.1 ◽

2021 ◽

Keyword(s):

North Atlantic ◽

Large Scale ◽

North Atlantic Ocean ◽

Atlantic Water ◽

Water Masses ◽

Buoyant Plume ◽

Freshwater Input ◽

The North ◽

Freshwater Source ◽

Lateral Mixing

Abstract Meltwater from Greenland is an important freshwater source for the North Atlantic Ocean, released into the ocean at the head of fjords in the form of runoff, submarine melt and icebergs. The meltwater release gives rise to complex in-fjord transformations that result in its dilution through mixing with other water masses. The transformed waters, which contain the meltwater, are exported from the fjords as a new water mass “Glacially Modified Water” (GMW). Here we use summer hydrographic data collected from 2013 to 2019 in Upernavik, a major glacial fjord in northwest Greenland, to describe the water masses that flow into the fjord from the shelf and the exported GMWs. Using an Optimum Multi-Parameter technique across multiple years we then show that GMW is composed of 57.8 ±8.1% Atlantic Water, 41.0 ±8.3% Polar Water, 1.0 ±0.1% subglacial discharge and 0.2 ±0.2% submarine meltwater. We show that the GMW fractional composition cannot be described by buoyant plume theory alone since it includes lateral mixing within the upper layers of the fjord not accounted for by buoyant plume dynamics. Consistent with its composition, we find that changes in GMW properties reflect changes in the AW and PW source waters. Using the obtained dilution ratios, this study suggests that the exchange across the fjord mouth during summer is on the order of 50 mSv (compared to a freshwater input of 0.5 mSv). This study provides a first order parameterization for the exchange at the mouth of glacial fjords for large-scale ocean models.

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