Reply to the Interactive comment on “Regional seesaw between North Atlantic and Nordic Seas during the last glacial abrupt climate events” by Mélanie Wary et al., by Anonymous Referee #3, Received and published: 26 March 2017

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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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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The role of volcanism for abrupt climate change during the last glacial period

10.5194/egusphere-egu2020-12846 ◽

2020 ◽

Author(s):

Anders Svensson ◽

Johannes Lohmann ◽

Sune Olander Rasmussen ◽

Christo Buizert

Keyword(s):

North Atlantic ◽

Ice Core ◽

Volcanic Eruptions ◽

Abrupt Climate Change ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Heinrich Events ◽

Climate Events ◽

The Last Glacial

During the last glacial period, abrupt climate events known as Dansgaard-Oeschger (DO) and Heinrich events have been observed in various types of Northern Hemispheric (NH) paleoclimate archives. It has been speculated that volcanism may play a role in the abrupt climate variability of the last glacial period, for example as a trigger of abrupt changes. The investigation of a possible link between abrupt climate events and volcanic eruptions has been hampered by the lack of a global volcanic eruption record from the last glacial period. A recent identification of 80 major bipolar volcanic eruptions in Greenland and Antarctic ice core records within the interval 12-60 ka BP now enables us to investigate this link.Using high-resolution ice-core records of climate (&#948;18O), atmospheric circulation changes (calcium) and volcanic eruptions (sulfate and other volcanic proxies) we investigate the timing of abrupt climate events and large volcanic eruptions at decadal resolution. We consider possible links between major volcanic eruptions and DO onsets (NH warming), DO terminations (NH cooling), and Heinrich stadials (strong NH cooling). Heinrich stadials are cold Greenland stadial periods during which Heinrich events occurred; large Hudson Strait iceberg discharge events that are characterized by deposition of significant amounts of ice rafted debris in North Atlantic marine sediments.Significant links of volcanic and climatic events are tested in a statistical framework under the null hypothesis of random and memoryless volcanic activity. Our analysis shows that while certainly not all abrupt climate change of the last glacial period is associated with volcanism, we find that volcanism may have induced some abrupt Greenland warming events and perhaps several of the extreme North Atlantic cold Heinrich stadials; no significant link is found between volcanism and DO terminations. We speculate that volcanic cooling can drive such transitions when the coupled system of Atlantic Ocean circulation and North Atlantic sea ice is close to a tipping point.

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