Warming of surface waters in the mid‐latitude North Atlantic during Heinrich events

Naafs, B. David A.; Hefter, Jens; Grützner, Jens; Stein, Rüdiger

doi:10.1029/2012pa002354

Cited by 66 publications

(53 citation statements)

References 110 publications

(166 reference statements)

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“…Neither of the experiments with only freshwater forcing can explain this change, indicating the important role for topography. Similarly, we find agreement with alkenone sea surface temperature, which shows warmer temperatures in the southern North Atlantic during HEs (38), only in those experiments in which the effect of ice sheet topography is included. Warm temperatures in this region were especially marked in those experiments in which both topographic and freshwater coupling were used, highlighting the need for coupled simulations of HE to correctly model these events.…”

Section: Paleoclimate Settingsupporting

confidence: 71%

Topography's crucial role in Heinrich Events

Roberts¹,

Valdes²,

Payne

2014

Proc. Natl. Acad. Sci. U.S.A.

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Heinrich Events, the abrupt changes in the Laurentide Ice Sheet that cause the appearance of the well-observed Heinrich Layers, are thought to have a strong effect on the global climate. The focus of most studies that have looked at the climate's response to these events has been the freshwater flux that results from melting icebergs. However, there is the possibility that the varying height of the ice sheet could force a change in the climate. In this study, we present results from a newly developed coupled climate/ ice sheet model to show what effect this topographic change has both on its own and in concert with the flux of freshwater from melting icebergs. We show that the topographic forcing can explain a number of the climate changes that are observed during Heinrich Events, such as the warming and wettening in Florida and the warm sea surface temperatures in the central North Atlantic, which freshwater forcing alone cannot. We also find regions, for example the tropical Atlantic, where the response is a mixture of the two: Here observations may help disentangle the relative importance of each mechanism. These results suggest that the simple paradigm of a Heinrich Event causing climate change via freshwater inputs into the North Atlantic needs to be revised.abrupt climate changes | ice sheet−climate interactions | North Atlantic E ver since anomalously thick layers of ice rafted debris were first observed in North Atlantic sediment cores (1), there has been a debate about both the cause of these Heinrich Layers (2-4) and what, if any, climatic changes they are associated with (5-7). In order for these layers of sediment to accumulate, a large number of sediment-bearing icebergs are required (8, 9). Because the overwhelming source of the sediment in these layers is Hudson Bay (10), an ice sheet instability in this region is the most likely cause. The exact mechanism causing this ice sheet instability is still uncertain, but most theories do agree that during the iceberg surge, the thickness of the ice sheet decreased significantly over Hudson Bay (2, 4). There are therefore two reasonably robust features of a Hudson Bay Heinrich Event (HE), the event that is ultimately responsible for the majority of each Heinrich Layer: a release of icebergs that then melt, and a reduction in the mass of the Laurentide Ice Sheet (LIS), which results in a reduction in the height of the ice sheet over Hudson Bay. Both of these are possible ways to force a change in the climate, hence the search for climate changes concomitant with HEs.Historically, the freshwater forcing from the melting icebergs has been viewed as the more important (11) climate forcing. It has been proposed that an injection of freshwater into the North Atlantic could interrupt the ocean's Meridional Overturning Circulation (MOC), which in turn could potentially alter the poleward transport of heat and thus cause a cooling in the North Atlantic (5, 6). However, there is also ample evidence that changing the height of the ice sheets over North America can c...

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Section: Paleoclimate Settingsupporting

confidence: 71%

Topography's crucial role in Heinrich Events

Roberts¹,

Valdes²,

Payne

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Higher temperatures (~1-3 °C) from ca. 15.2 to 14.5 ka appear to correspond to pre-Bølling-Allerød (B/A) warming or late Heinrich 1 warming, as recorded in the mid-latitude North Atlantic (Naafs et al, 2013). During the B/A, from 14.5 to 12.6 ka temperatures were higher, varying between 4 °C and 8 °C.…”

Section: Resultsmentioning

confidence: 99%

Atmospheric connections with the North Atlantic enhanced the deglacial warming in northeast China

Zheng

Pancost

Liu

et al. 2017

Geology

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Variations in atmospheric circulation across the last deglaciation in the northernmost monsoon-influenced regions of Asia are not well constrained, highlighting a fundamental gap in our understanding of Asian climate. Here we reconstruct continental air temperatures for northeast China across the last deglaciation (past 16 k.y.), based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers in a sequence of the Hani peat (Jilin Province, northeast China). Our results indicate large (as much as 10 °C) oscillations in temperature in northeast China across the deglaciation, oscillations significantly larger than observed in other temperature records from low-latitude or same-latitude East Asia, but consistent with climate model simulations. This enhanced magnitude, as well as the timing of temperature variations, provides evidence for atmospheric teleconnections with high latitudes; in particular, we suggest that highlatitude cooling associated with Arctic ice expansion and changes in Atlantic Meridional Overturning Circulation enhanced the intensity and lowered the temperature of Eurasian mid-latitude westerlies and northwesterly winds over East Asia during the last glacial, delivering cold air masses to northeast China. During the deglaciation the westerlies and therefore delivery of cold air masses weakened, amplifying the deglacial warming in this region. We conclude that changes in North Atlantic climate had a particularly strong impact on the northernmost parts of the East Asian monsoon-influenced area.

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“…Although the jet stream likely was stronger and more zonal across the North Atlantic during YDS winters on account of expanded sea-ice (9), retreat of the sea-ice edge during spring and summer to a position north of Norway (31) could have facilitated a more meridional trajectory of the summertime jet, resulting in incursions of warmer subtropical air masses to Scotland. Additionally, YDS warming of the midlatitude North Atlantic that arose as a consequence of curtailed MOC (32) would have enhanced warming of subtropical air masses, potentially stimulating summertime melting of downwind European glaciers. Concurrently, increasing radiative heating due to maximum summer insolation, combined with rising atmospheric CO 2 concentrations (33), could have dominated seasonal warming and glacier recession during the YDS.…”

Section: N O R T H a T L A N T I C C U R R E N Tmentioning

confidence: 99%

Younger Dryas deglaciation of Scotland driven by warming summers

Bromley

Putnam

Rademaker

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The Younger Dryas Stadial (YDS; ∼12,900-11,600 y ago) in the Northern Hemisphere is classically defined by abrupt cooling and renewed glaciation during the last glacial-interglacial transition. Although this event involved a global reorganization of atmospheric and oceanic circulation [Denton GH, Alley RB, Comer GC, Broecker WS (2005) Quat Sci Rev 24:1159-1182], the magnitude, seasonality, and geographical footprint of YDS cooling remain unresolved and pose a challenge to our understanding of abrupt climate change. Here, we present a deglacial chronology from Scotland, immediately downwind of the North Atlantic Ocean, indicating that the Scottish ice cap disintegrated during the first half of the YDS. We suggest that stratification of the North Atlantic Ocean resulted in amplified seasonality that, paradoxically, stimulated a severe wintertime climate while promoting warming summers through solar heating of the mixed layer. This latter process drove deglaciation of downwind landmasses to completion well before the end of the YDS.

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Warming of surface waters in the mid‐latitude North Atlantic during Heinrich events

Cited by 66 publications

References 110 publications

Topography's crucial role in Heinrich Events

Topography's crucial role in Heinrich Events

Atmospheric connections with the North Atlantic enhanced the deglacial warming in northeast China

Younger Dryas deglaciation of Scotland driven by warming summers

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