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

1997 ◽  
Vol 47 (2) ◽  
pp. 218-234 ◽  
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.

scholarly journals Hydrological instability during the Last Interglacial in central Asia: a new diatom oxygen isotope record from Lake Baikal

2013 ◽  
Vol 66 ◽  
pp. 45-54 ◽  
Author(s):  
Anson W. Mackay ◽  
George E.A. Swann ◽  
Nathalie Fagel ◽  
Susanne Fietz ◽  
Melanie J. Leng ◽  
...  
Keyword(s):  
Central Asia ◽  
Oxygen Isotope ◽  
Lake Baikal ◽  
Last Interglacial ◽  
Oxygen Isotope Record ◽  
Isotope Record

Middle Pleistocene age of the Nome River glaciation, northwestern Alaska

1991 ◽  
Vol 36 (3) ◽  
pp. 277-293 ◽  
Author(s):  
Darrell S. Kaufman ◽  
Robert C. Walter ◽  
Julie Brigham-Grette ◽  
David M. Hopkins
Keyword(s):  
Middle Pleistocene ◽  
Laser Fusion ◽  
Basaltic Lava ◽  
Last Interglacial ◽  
Oxygen Isotope Record ◽  
Isotope Record ◽  
Order Of Magnitude ◽  
Nearshore Sediments ◽  
The Mean ◽  
Basaltic Lava Flow

AbstractDuring the middle Pleistocene Nome River glaciation of northwestern Alaska, glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals. The age of the Nome River glaciation is constrained by laser-fusion 40Ar/39Ar analyses of basaltic lava that overlies Nome River drift at Minnie Creek, central Seward Peninsula, that average 470,000 ± 190,000 yr (±1σ). Milligram-size subsamples of the lava were dated to identify and eliminate extraneous 40Ar enrichments that rendered the mean of conventional K-Ar dates on larger bulk samples of the same flow too old (700,000 ± 570,000 yr). While the 40Ar/39Ar analyses provide a minimum limiting age for the Nome River glaciation, maximum ages are provided by a provisional K-Ar date on a basaltic lava flow that underlies the Nome River drift at nearby Lave Creek, by paleomagnetic determinations of the drift itself at and near the type locality, and by amino acid epimerization analysis of molluscan fossils from nearshore sediments of the Anvilian marine transgression that underlie Nome River drift on the coastal plain at Nome. Taken together, the new age data indicate that the glaciation took place between 580,000 and 280,000 yr ago. The altitude of the Anvilian deposits suggests that eustatic sea level during the Anvilian transgression rose at least as high as and probably higher than during the last interglacial transgression; by correlation with the marine oxygen-isotope record, the transgression probably dates to stage 11 at 410,000 yr, and the Nome River glaciation is younger still. Analyses of floor altitudes of presumed Nome River cirques indicate that the Nome River regional snowline depression was at least twice that of the maximum late Wisconsin. The cause of the enhanced snowline lowering appears to be related to greater availability of moisture in northwestern Alaska during the middle Pleistocene.

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

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. 

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

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?

scholarly journals Export of ice sheet meltwater from Upernavik Fjord, West Greenland

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.

scholarly journals An oxygen isotope record of lacustrine opal from a European Maar indicates climatic stability during the Last Interglacial

2001 ◽  
Vol 28 (12) ◽  
pp. 2305-2308 ◽  
Author(s):  
Aldo Shemesh ◽  
Miri Rietti-Shati ◽  
Patrick Rioual ◽  
Rick Battarbee ◽  
Jacques-Louis de Beaulieu ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Last Interglacial ◽  
Oxygen Isotope Record ◽  
Isotope Record

Oceanography of the Western Interior Seaway during OAE 2 using Nd isotopes

2020 ◽  
Author(s):  
Sietske Batenburg ◽  
Hugh Jenkyns ◽  
Raquel Bryant ◽  
Mark Leckie ◽  
Alexander Dickson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Ocean Circulation ◽  
Volcanic Rocks ◽  
Source Area ◽  
High Arctic ◽  
Water Masses ◽  
Western Interior Seaway ◽  
Mass Source ◽  
Cold Event ◽  
The North

&lt;p&gt;During the greenhouse climate of the mid-Cretaceous, the Western Interior Seaway (WIS) experienced semi-restricted conditions with poor water-column ventilation, leading to the accumulation of black organic-rich shales. In the Maverick Basin, the southernmost extent of the WIS, the main phase of organic-matter deposition occurred in the early to late Cenomanian, before Oceanic Anoxic Event 2 (OAE 2). A sea-level rise prior to the event may have caused the basin to become better ventilated during the Cenomanian&amp;#8211;Turonian transition, and ocean circulation likely played a major role on productivity and the preservation of organic matter. Widely different regimes of ocean circulation are suggested to have operated, with alternating incursions of water masses from both the north and the south. Foraminiferal assemblages suggest that during the early phase of OAE 2, Tethyan waters were drawn northward into the WIS (Elderbak &amp; Leckie, 2016), whereas dinocyst occurrences indicate an influx of boreal surface waters into the Maverick Basin at that time (Eldrett et al., 2014; 2017). This cooler episode correlates with the so-called Plenus Cold Event, recognized in northern Europe by southward invasion of boreal faunas.&lt;/p&gt;&lt;p&gt;Here we present neodymium-isotope records (&amp;#949;&lt;sub&gt;Nd&lt;/sub&gt;) of fish teeth and detrital fractions from the Eagle Ford Formation that record the presence of distinct water masses at depth and allow testing of suggested mechanisms of ocean circulation. Mid- to late Cenomanian values of &amp;#949;&lt;sub&gt;Nd&lt;/sub&gt; around -3 (this study) are unusually radiogenic compared to coeval open ocean &amp;#949;&lt;sub&gt;Nd&lt;/sub&gt; records from the North Atlantic, where values typically lie between -4 and -10 (Martin et al., 2012, Robinson &amp; Vance, 2012) and may reflect a strong influence of regional volcanism close to the WIS and/or weathering of mafic volcanic rocks in the water-mass source area. An excursion to positive &amp;#949;&lt;sub&gt;Nd&lt;/sub&gt; values in the WIS during OAE 2 may reflect changes in local weathering, or alternatively, the incursion of water masses carrying a signature of volcanic activity. The coeval emplacement of several Large Igneous Provinces (LIP), including the High Arctic LIP (Estrada et al., 2015) and the Caribbean LIP, may have influenced the seawater chemistry of the WIS, as reflected in Os and Cr concentrations and isotope ratios from the USGS Portland core (Du Vivier et al., 2014; Holmden et al., 2016).&amp;#160; Comparison of seawater and detrital &amp;#949;&lt;sub&gt;Nd&lt;/sub&gt; signatures with records north and south of the Maverick Basin will elucidate the direction and degree of deep-water exchange in the southern WIS.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Du Vivier, A.D.C. et al., 2014, EPSL, 389, 23-33&lt;/p&gt;&lt;p&gt;Elderbak, K. &amp; Leckie, R.M., 2016. Cret. Res., 60, pp.52-77.&lt;/p&gt;&lt;p&gt;Eldrett, J.S., et al., 2014. Geology, 42(7), pp.567-570.&lt;/p&gt;&lt;p&gt;Eldrett, J.S., et al., 2017. Climate of the Past (13), pp.855&amp;#8211;878.&lt;/p&gt;&lt;p&gt;Estrada, 2015. Int. J. Earth Sci. (104), pp.1981&amp;#8211;2005.&lt;/p&gt;&lt;p&gt;Holmden et al., 2016. Geochim. Cosmochim. Acta 186 (2016) 277&amp;#8211;295&lt;/p&gt;&lt;p&gt;Martin, E.E., et al., 2012. EPSL, 327, pp.111-120.&lt;/p&gt;&lt;p&gt;Robinson, S.A. &amp; Vance, D., 2012. Paleoceanography, 27(1).&lt;/p&gt;

scholarly journals Observed trends of anthropogenic acidification in North Atlantic water masses

2012 ◽  
Vol 9 (3) ◽  
pp. 3003-3030
Author(s):  
M. Vázquez-Rodríguez ◽  
F. F. Pérez ◽  
A. Velo ◽  
A. F. Ríos ◽  
H. Mercier
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Deep Convection ◽  
Temporal Trends ◽  
Atlantic Water ◽  
Water Masses ◽  
The North ◽  
Iceland Basin ◽  
The North Atlantic ◽  
Atmospheric Co2 Concentrations

Abstract. The lack of observational pH data has made difficult assessing recent rates of ocean acidification, particularly in the high latitudes. Here we present a time series of high-quality carbon system measurements in the North Atlantic, comprising fourteen cruises spanning over 27 yr (1981–2008) and covering important water mass formation areas like the Irminger and Iceland basins. We provide direct quantification of anthropogenic acidification rates in upper and intermediate North Atlantic waters by removing the natural variability of pH from the observations. Bottle data were normalised to basin-average conditions using climatological data and further condensed into averages per water mass and year to examine the temporal trends. The highest acidification rates of all inspected water masses were associated with surface waters in the Irminger Sea (−0.0018 ± 0.0001 yr−1) and the Iceland Basin (−0.0012 ± 0.0002 yr−1) and, unexpectedly, with Labrador Seawater (LSW) which experienced an unprecedented pH drop of −0.0015 ± 0.001 yr−1. The latter stems from the formation by deep convection and the rapid propagation in the North Atlantic subpolar gyre of this well-ventilated water mass. The high concentrations of anthropogenic CO2 are effectively transported from the surface into intermediate waters faster than via downward diffusion, thus accelerating the acidification rates of LSW. An extrapolation of the observed lineal trends of acidification suggests that the pH of LSW could drop 0.45 units with respect to pre-industrial levels by the time atmospheric CO2 concentrations double the present ones.

scholarly journals Trends of anthropogenic CO<sub>2</sub> storage in North Atlantic water masses

2010 ◽  
Vol 7 (5) ◽  
pp. 1789-1807 ◽  
Author(s):  
F. F. Pérez ◽  
M. Vázquez-Rodríguez ◽  
H. Mercier ◽  
A. Velo ◽  
P. Lherminier ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Atlantic Water ◽  
Average Concentration ◽  
Rate Of Change ◽  
Point Of View ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The North ◽  
The North Atlantic

Abstract. A high-quality inorganic carbon system database, spanning over three decades (1981–2006) and comprising of 13 cruises, has allowed the applying of the φC°T method and coming up with estimates of the anthropogenic CO2 (Cant) stored in the main water masses of the North Atlantic. In the studied region, strong convective processes convey surface properties, like Cant, into deeper ocean layers and grants this region an added oceanographic interest from the point of view of air-sea CO2 exchanges. Generally, a tendency for decreasing Cant storage rates towards the deep layers has been observed. In the Iberian Basin, the North Atlantic Deep Water has low Cant concentrations and negligible storage rates, while the North Atlantic Central Water in the upper layers shows the largest Cant values and the largest annual increase of its average concentration (1.13 ± 0.14 μmol kg−1 yr−1). This unmatched rate of change in the Cant concentration of the warm upper limb of the Meridional Overturning Circulation decreases towards the Irminger basin (0.68 ± 0.06 μmol kg−1 yr−1) due to the lowering of the buffering capacity. The mid and deep waters in the Irminger Sea show rather similar Cant concentration rates of increase (between 0.33 and 0.45 μmol kg−1 yr−1), whereas in the Iceland basin these layers seem to have been less affected by Cant. Overall, the Cant storage rates in the North Atlantic subpolar gyre during the first half of the 1990s, when a high North Atlantic Oscillation (NAO) phase was dominant, are ~48% higher than during the 1997–2006 low NAO phase that followed. This result suggests that a net decrease in the strength of the North Atlantic sink of atmospheric CO2 has taken place during the present decade. The changes in deep-water ventilation are the main driving processes causing this weakening of the North Atlantic CO2 sink.

Éléments d'une climatostratigraphie du Pléistocène moyen et tardif dans l'est du Canada par l'analyse palynologique et isotopique du forage 84-030-003, mer du Labrador

1987 ◽  
Vol 24 (9) ◽  
pp. 1886-1902 ◽  
Author(s):  
A. de Vernal ◽  
C. Hillaire-Marcel
Keyword(s):  
North Atlantic ◽  
Strong Relationship ◽  
Atlantic Water ◽  
Water Masses ◽  
Labrador Sea ◽  
Aeolian Transport ◽  
Eastern Canada ◽  
The North ◽  
Labrador Current ◽  
Isotopic Analyses

The piston and gravity cores 84-030-003, collected in the southern Labrador Sea, have been sampled for detailed palynological and isotopic analyses. The δ18O record on foraminifera (Neogloboquadrina pachyderma, left-coiling) indicates a stratigraphy spanning isotopic stages 8 to 1, i.e., over ca. 300 000 years. The isotopic record allows the calculation of a mean sedimentation rate of approximately 5 cm/ka.The pollen and spore contents of the sediments are low. The low pollen influxes (generally less than 1 grain/cm2 per year) and the dominance of Pinus suggest aeolian transport over long distances with southwest–northeast to south-southwest–north-northeast trends. Dinoflagellate cyst concentrations are relatively low, indicating a low regional phytoplanktonic productivity. The assemblages are, however, diversified. They reflect influences from the North Atlantic Drift and from the Labrador Current. The occurrence of warm-temperate to tropical Impagidinium species in deposits suggests an almost permanent penetration of North Atlantic water masses into the Labrador Sea during the middle and Late Pleistocene. This divergence was apparently interrupted during the last glacial maximum of isotopic stage 2. Increases in the concentration of dinocysts such as Operculodinium centrocarpum, Nematosphaeropsis labyrinthea, and Bitectatodinium tepikiense were recorded during interglacial maxima of stages 7, 5, and 1. These dinocyst peaks indicate a high primary productivity and cool-temperate to subarctic conditions in surficial water masses offshore eastern Canada. In addition, they are probably related to a strong hydrodynamic regime of the Labrador Current. Fluctuations in the dinocyst concentrations are in most cases synchronous with the δ18O changes of foraminifera, indicating a strong relationship between the paleo-oceanography of the Labrador Sea and the Quaternary glaciations.

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