North Atlantic deep water sources and export since MIS3: implications from Nd isotopes

Deep water formation in the North Atlantic represents an integral link between the atmosphere, cryosphere, and the deep ocean: heat loss from warm surface waters supplies moisture to the high latitudes and their subsequent sinking ventilates the deep ocean and sequesters greenhouse gases from the atmosphere. This moisture supply supported the formation of immense ice sheets in the region during the last glacial, which in turn affected climate. While many studies have improved our understanding of these processes for past glacials, a comprehensive picture including the significance and variation of deep water export from the Nordic Seas is still missing. Furthermore, recent observations suggested the export of a previously unknown bottom water mass from the glacial subpolar North Atlantic.In this study we investigate the distribution and sourcing of water masses in the subpolar North Atlantic since MIS3 with the help of authigenic Nd isotopes. This method benefits from the large heterogeneity in Nd isotopic compositions of source rocks in this region, but the post-depositional dissolution of detritus within the sediments can also impede interpretations of individual records. We thus compare several Nd isotope records from the subpolar North Atlantic and Nordic Seas in order to define distinct deep water mass end members and estimate their prevalence and mixing in the subpolar North Atlantic during the last 30 ka. Our observations suggest that Nordic Seas deep water overflowing the Greenland-Scotland Ridge during MIS2 reached into the deep subpolar North Atlantic. Furthermore, its spatial distribution implies that overflow across Denmark Strait into the Irminger Basin was more pronounced than overflow into the Iceland Basin further south. The hydrographic configuration during the Last Glacial Maximum thus appears to have been more complex and more similar to today than previously thought.

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A weaker Atlantic Meridional Overturning Circulation at the Last Glacial Maximum led to a greater deep ocean carbon content

10.5194/egusphere-egu2020-2920 ◽

2020 ◽

Author(s):

Laurie Menviel ◽

Paul Spence ◽

Luke Skinner ◽

Kazuyo Tachikawa ◽

Tobias Friedrich ◽

...

Keyword(s):

Last Glacial Maximum ◽

North Atlantic ◽

Deep Ocean ◽

Glacial Maximum ◽

Last Glacial ◽

The North ◽

The North Atlantic ◽

Ocean Carbon ◽

The Last Glacial Maximum ◽

The Last Glacial

While paleoproxy records and modelling studies consistently suggest that North Atlantic&#160; Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than during pre-industrial times, its strength is still subject to debate partly due to different signals across the North Atlantic. Here, using a series of LGM experiments performed with a carbon isotopes enabled Earth system model, we show that proxy records are consistent with a shallower and weaker NADW. A significant equatorward advance of sea-ice over the Labrador Sea and the Nordic Seas shifts the NADW convection sites to the south of the Norwegian Sea. While the deep western boundary current in the Northwest Atlantic weakens with NADW, a change in density gradients strengthens the deep southward flow in the Northeast Atlantic. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic despite its transport being reduced. This resultant globally weaker oceanic circulation leads to an increase in deep ocean carbon of ~500 GtC, thus significantly contributing to the lower LGM atmospheric CO2 concentration.&#160;

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Deep-water mass source and dynamic associated with rapid climatic variations during the last glacial stage in the North Atlantic: A multiproxy investigation of the detrital fraction of deep-sea sediments

Geochemistry Geophysics Geosystems ◽

10.1029/2005gc001070 ◽

2006 ◽

Vol 7 (2) ◽

pp. n/a-n/a ◽

Cited By ~ 27

Author(s):

M. Ballini ◽

C. Kissel ◽

C. Colin ◽

T. Richter

Keyword(s):

North Atlantic ◽

Deep Water ◽

Deep Sea ◽

Water Mass ◽

Mass Source ◽

Climatic Variations ◽

The North ◽

Glacial Stage ◽

The North Atlantic ◽

The Last Glacial

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Regional seesaw between the North Atlantic and Nordic Seas during the last glacial abrupt climate events

Climate of the Past ◽

10.5194/cp-13-729-2017 ◽

2017 ◽

Vol 13 (6) ◽

pp. 729-739 ◽

Cited By ~ 4

Author(s):

Mélanie Wary ◽

Frédérique Eynaud ◽

Didier Swingedouw ◽

Valérie Masson-Delmotte ◽

Jens Matthiessen ◽

...

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Sea Surface ◽

Nordic Seas ◽

Norwegian Sea ◽

Surface Conditions ◽

Last Glacial ◽

The North ◽

The North Atlantic ◽

The Last Glacial

Abstract. Dansgaard–Oeschger oscillations constitute one of the most enigmatic features of the last glacial cycle. Their cold atmospheric phases have been commonly associated with cold sea-surface temperatures and expansion of sea ice in the North Atlantic and adjacent seas. Here, based on dinocyst analyses from the 48–30 ka interval of four sediment cores from the northern Northeast Atlantic and southern Norwegian Sea, we provide direct and quantitative evidence of a regional paradoxical seesaw pattern: cold Greenland and North Atlantic phases coincide with warmer sea-surface conditions and shorter seasonal sea-ice cover durations in the Norwegian Sea as compared to warm phases. Combined with additional palaeorecords and multi-model hosing simulations, our results suggest that during cold Greenland phases, reduced Atlantic meridional overturning circulation and cold North Atlantic sea-surface conditions were accompanied by the subsurface propagation of warm Atlantic waters that re-emerged in the Nordic Seas and provided moisture towards Greenland summit.

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120,000 year record of sea ice in the North Atlantic

10.5194/cp-2018-80 ◽

2018 ◽

Cited By ~ 2

Author(s):

Niccolò Maffezzoli ◽

Paul Vallelonga ◽

Ross Edwards ◽

Alfonso Saiz-Lopez ◽

Clara Turetta ◽

...

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Arctic Sea Ice ◽

Sea Ice Extent ◽

Nordic Seas ◽

Last Glacial ◽

The North ◽

Arctic Sea ◽

The North Atlantic ◽

The Last Glacial

Abstract. Although it has been demonstrated that the speed and magnitude of recent Arctic sea ice decline is unprecedented for the past 1,450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Here we present a 120 kyr record of bromine enrichment from the RECAP ice core, coastal East Greenland, and reconstruct past sea ice conditions in the North Atlantic as far north as the entrance of the Arctic Ocean (50–85° N). Bromine enrichment has been previously employed to reconstruct first-year sea ice (FYSI) in the Canadian Arctic over the last glacial cycle. We find that during the last deglaciation, the transition from multi-year sea ice (MYSI) to FYSI started at ∼ 17.6 kyr, synchronous with sea ice reductions observed in the eastern Nordic seas (Müller and Stein, 2014; Hoff et al., 2016) and with the increase of North Atlantic ocean temperature (Dokken and Jansen, 1999). FYSI reached its maximum extent at 12.4–11.8 kyr, after which open-water conditions started to dominate, as supported by sea ice records from the eastern Nordic seas and the North Icelandic shelf. Our results show that over the last 120,000 years, sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and MIS4, with decreased levels during MIS3 and the onset of the last glacial period (late-MIS5). Sea ice extent during the last 10 kyr (Holocene/MIS1) has been less than at any time in the last 120 kyr.

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Surface and deep water circulation in late Cretaceous North Atlantic greenhouse ocean

10.32469/10355/9665 ◽

2009 ◽

Author(s):

◽

Carolina Isaza LondonÌƒo

Keyword(s):

Ocean Circulation ◽

Late Cretaceous ◽

North Atlantic ◽

Deep Water ◽

Water Mass ◽

Deep Ocean ◽

Water Circulation ◽

Regional Warming ◽

The North ◽

The North Atlantic

This research provides the first of its kind empirical data regarding the evolution of Maastrichtian surface to deep ocean circulation in the North Atlantic. Differences in foraminiferal abundances and oxygen and carbon isotopic ratios of bulk carbonate and foraminifera between two Ocean Drilling Program Sites in the subtropical North Atlantic indicate a sharp water mass boundary was a relatively stable and persistent feature of the Maastrichtian North Atlantic despite significant regional warming across the interval. Neodymium isotopes of fish debris, on the other hand, indicate significant changes in intermediate and deep water circulation through the Late Cretaceous and especially during the Maastrichtian. During the Cenomanian-Campanian interval at least three different deep water masses were active in the North Atlantic including one formed by downwelling of warm saline waters in the Demerara Rise region. During the Campanian-Maastrichtian, low-latitude-sourced waters seem to have reached abyssal depths, but from the mid-Maastrichtian on, this water mass seems to have declined in importance. From the mid-Danian on, we found evidence for only one water mass (plausibly sourced in the northern North Atlantic, as it is today) at bathyal and abyssal depths in the North Atlantic. Our data demonstrate that surface and, especially, intermediate and deep water circulation patterns are an important (and measurable) variable that helps determine greenhouse temperature distributions on regional and global scales.

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Evidence for strong relations between the upper Tagus loess formation (central Iberia) and the marine atmosphere off the Iberian margin during the last glacial period

Quaternary Research ◽

10.1017/qua.2020.119 ◽

2021 ◽

pp. 1-30

Author(s):

Daniel Wolf ◽

Thomas Kolb ◽

Karolin Ryborz ◽

Susann Heinrich ◽

Imke Schäfer ◽

...

Keyword(s):

North Atlantic ◽

Moisture Transfer ◽

Sea Temperature ◽

Last Glacial ◽

Atmospheric Circulation Patterns ◽

The North ◽

Terrestrial Environments ◽

The North Atlantic ◽

Iberian Margin ◽

The Last Glacial

Abstract During glacial times, the North Atlantic region was affected by serious climate changes corresponding to Dansgaard-Oeschger cycles that were linked to dramatic shifts in sea temperature and moisture transfer to the continents. However, considerable efforts are still needed to understand the effects of these shifts on terrestrial environments. In this context, the Iberian Peninsula is particularly interesting because of its close proximity to the North Atlantic, although the Iberian interior lacks paleoenvironmental information so far because suitable archives are rare. Here we provide an accurate impression of the last glacial environmental developments in central Iberia based on comprehensive investigations using the upper Tagus loess record. A multi-proxy approach revealed that phases of loess formation during Marine Isotope Stage (MIS) 2 (and upper MIS 3) were linked to utmost aridity, coldness, and highest wind strengths in line with the most intense Greenland stadials also including Heinrich Events 3–1. Lack of loess deposition during the global last glacial maximum (LGM) suggests milder conditions, which agrees with less-cold sea surface temperatures (SST) off the Iberian margin. Our results demonstrate that geomorphological system behavior in central Iberia is highly sensitive to North Atlantic SST fluctuations, thus enabling us to reconstruct a detailed hydrological model in relation to marine–atmospheric circulation patterns.

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Timing and structure of the Younger Dryas event and its underlying climate dynamics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2007869117 ◽

2020 ◽

Vol 117 (38) ◽

pp. 23408-23417

Author(s):

Hai Cheng ◽

Haiwei Zhang ◽

Christoph Spötl ◽

Jonathan Baker ◽

Ashish Sinha ◽

...

Keyword(s):

Southern Hemisphere ◽

North Atlantic ◽

Time Scale ◽

Asian Monsoon ◽

Younger Dryas ◽

Tropical Pacific ◽

Last Glacial ◽

The North ◽

The North Atlantic ◽

The Last Glacial

The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard–Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic–Asian Monsoon-Westerlies directionality of climatic recovery.

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The Effect of a Large Freshwater Perturbation on the Glacial North Atlantic Ocean Using a Coupled General Circulation Model

Journal of Climate ◽

10.1175/jcli3867.1 ◽

2006 ◽

Vol 19 (17) ◽

pp. 4436-4447 ◽

Cited By ~ 16

Author(s):

C. D. Hewitt ◽

A. J. Broccoli ◽

M. Crucifix ◽

J. M. Gregory ◽

J. F. B. Mitchell ◽

...

Keyword(s):

Sea Ice ◽

North Atlantic ◽

General Circulation ◽

Circulation Model ◽

Quasi Equilibrium ◽

Last Glacial ◽

Proxy Records ◽

The North ◽

The North Atlantic ◽

The Last Glacial

Abstract The commonly held view of the conditions in the North Atlantic at the last glacial maximum, based on the interpretation of proxy records, is of large-scale cooling compared to today, limited deep convection, and extensive sea ice, all associated with a southward displaced and weakened overturning thermohaline circulation (THC) in the North Atlantic. Not all studies support that view; in particular, the “strength of the overturning circulation” is contentious and is a quantity that is difficult to determine even for the present day. Quasi-equilibrium simulations with coupled climate models forced by glacial boundary conditions have produced differing results, as have inferences made from proxy records. Most studies suggest the weaker circulation, some suggest little or no change, and a few suggest a stronger circulation. Here results are presented from a three-dimensional climate model, the Hadley Centre Coupled Model version 3 (HadCM3), of the coupled atmosphere–ocean–sea ice system suggesting, in a qualitative sense, that these diverging views could all have occurred at different times during the last glacial period, with different modes existing at different times. One mode might have been characterized by an active THC associated with moderate temperatures in the North Atlantic and a modest expanse of sea ice. The other mode, perhaps forced by large inputs of meltwater from the continental ice sheets into the northern North Atlantic, might have been characterized by a sluggish THC associated with very cold conditions around the North Atlantic and a large areal cover of sea ice. The authors’ model simulation of such a mode, forced by a large input of freshwater, bears several of the characteristics of the Climate: Long-range Investigation, Mapping, and Prediction (CLIMAP) Project’s reconstruction of glacial sea surface temperature and sea ice extent.

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Northern Sourced Water dominated the Atlantic Ocean during the Last Glacial Maximum

10.5194/egusphere-egu2020-1353 ◽

2020 ◽

Author(s):

Frerk Pöppelmeier ◽

Patrick Blaser ◽

Marcus Gutjahr ◽

Samuel Jaccard ◽

Martin Frank ◽

...

Keyword(s):

Carbon Storage ◽

Last Glacial Maximum ◽

Water Mass ◽

Stable Carbon Isotope ◽

Deep Ocean ◽

Glacial Maximum ◽

Ice Age ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO2 concentrations. This carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here we present new sediment derived bottom water neodymium isotope data that allow fingerprinting of water masses and their mixtures and provide a more complete picture of the Atlantic overturning circulation geometry during the Last Glacial Maximums. These results suggest that the vertical and meridional structure of the Atlantic deep water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern sourced water substantially expanding to shallower depths and farther into the northern hemisphere than today, which has been inferred from stable carbon isotope reconstructions. We argue that depleted &#948;13C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern sourced water. Instead, these values may represent a northern sourced water mass with lower than modern preformed &#948;13C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation. If proven to be correct, the glacial water mass structure inferred from Nd isotopes has profound implications on our understanding of the deep ocean carbon storage during the Last Glacial Maximum.

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