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

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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Decoupling of surface ocean hydrology and Greenland ice core records in the eastern North Atlantic during the last glacial inception

10.5194/egusphere-egu21-16262 ◽

2021 ◽

Author(s):

Svetlana Radionovskaya ◽

Luke Skinner ◽

Mervyn Greaves

Keyword(s):

Climate Variability ◽

North Atlantic ◽

Benthic Foraminifera ◽

Ice Cores ◽

Last Glacial ◽

Surface Ocean ◽

The North ◽

The North Atlantic ◽

Iberian Margin ◽

The Last Glacial

MIS 4, a key paleoclimatic interval for the last glacial inception, is characterized by a rapid CO2 drop of approx. ~28ppm and a large drop in temperature (as seen in Antarctic ice cores). SSTs in the North Atlantic are thought to be coupled to AMOC strength, whereby various proxies suggest a weaker and shoaled AMOC during the transition from MIS5a to MIS4. Furthermore, several millennial events also occurred during MIS 4, including Heinrich Stadial 6 and DO events 16-19. MIS 4 is thus an ideal interval to study and eventually to disentangle, glacial-interglacial and millennial variability.Here, we present high resolution planktonic and benthic foraminifera geochemical data from several marine sediment cores from the Iberian Margin (including stable isotope and trace element data). The Iberian Margin is a prime location to study millennial-scale climate variability as isotope records of planktonic and benthic foraminifera simultaneously recorded rapid climate change expressed in Greenland and Antarctic ice cores, respectively, during the last glacial period. However, our results so far, suggest that surface ocean response at this site does not track Greenland temperature, as would be expected for this region of the North Atlantic. Perhaps the most striking, our planktic Mg/Ca record shows a late onset of rapid MIS 4 cooling at the start of Heinrich 6, and no clear millennial variability signal. This is in agreement with SST reconstructed using alkenones (Pailler and Bard, 2002) and planktonic foraminifera faunal assemblages (Salgueiro et al., 2010) from nearby core sites. Local d18O seawater reconstructions imply major hydrological changes in the region, which is supported by the &#8220;dry event&#8221; seen in speleothems from North Eastern Iberia (Perez-Mehias et al., 2019) and Italy (Columbu et al., 2020), just before Heinrich 6. We propose that the observed changes may reflect changes in regional ocean and atmospheric circulation patterns such as the interaction of the strength and position of the Azores Current, Iberian Poleward Current and the Subtropical Gyre, which in turn could depend on the larger scale AMOC and wind driven surface ocean changes due to glacial-interglacial and millennial variability. Further links to moisture transport, ice sheet growth and carbon cycle are yet to be investigated.&#160;ReferencesColumbu, A., Chiarini, V., Sp&#246;tl, C., Benazzi, S., Hellstrom, J., Cheng, H. and De Waele, J., 2020. Speleothem record attests to stable environmental conditions during Neanderthal&#8211;modern human turnover in southern Italy.&#160;Nature Ecology & Evolution, 4(9), pp.1188-1195.Pailler, D. and Bard, E., 2002. High frequency palaeoceanographic changes during the past 140&#8200;000 yr recorded by the organic matter in sediments of the Iberian Margin.&#160;Palaeogeography, Palaeoclimatology, Palaeoecology, 181(4), pp.431-452.P&#233;rez-Mej&#237;as, C., Moreno, A., Sancho, C., Mart&#237;n-Garc&#237;a, R., Sp&#246;tl, C., Cacho, I., Cheng, H. and Edwards, R., 2019. Orbital-to-millennial scale climate variability during Marine Isotope Stages 5 to 3 in northeast Iberia.&#160;Quaternary Science Reviews, 224, p.105946.Salgueiro, E., Voelker, A., de Abreu, L., Abrantes, F., Meggers, H. and Wefer, G., 2010. Temperature and productivity changes off the western Iberian margin during the last 150&#160;ky.&#160;Quaternary Science Reviews, 29(5-6), pp.680-695.

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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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Climatic Record of the Past 130,000 Years in North Atlantic Deep-Sea Core V23-82: Correlation with the Terrestrial Record

Quaternary Research ◽

10.1016/0033-5894(73)90057-4 ◽

1973 ◽

Vol 3 (1) ◽

pp. 110-116 ◽

Cited By ~ 70

Author(s):

Constance Sancetta ◽

John Imbrie ◽

N.G. Kipp

Keyword(s):

North Atlantic ◽

Deep Sea ◽

Planktonic Foraminifera ◽

Linear Interpolation ◽

Stratigraphic Correlation ◽

Last Glacial ◽

The Past ◽

The North ◽

The North Atlantic ◽

The Last Glacial

AbstractQuantitative paleo-environmental analyses of planktonic foraminifera in 182 samples covering the past 130,000 years in North Atlantic deep-sea core V23-82 yield time series interpreted in terms of changing surface-water conditions. An absolute chronology is estimated by linear interpolation between levels dated by 14C or by stratigraphic correlation with other radiometrically dated climatic records. Significant events include: (1) rapid warming at 127,000 YBP, marking the start of the penultimate North Atlantic and European interglacial; (2) 124,000 YBP temperature maximum (Eemian); (3) 109,000 YBP cooling, correlated with the beginning of the last European glaciation (Würm), and representing a temporary cooling of the North Atlantic; (4) severe cooling 73,000 YBP, marking the start of the last full glacial regime in the North Atlantic; (5) short warm intervals within the last glacial regime dated at 59,000 YBP, 48,000 YBP, and 31,000 YBP; (6) rapid termination of the last glacial interval at 11,000 YBP; (7) a 6000 YBP hypsi-saline, followed by lowering salinity values presumably associated with decreasing flux of Gulf Stream waters over the core site.

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