1/29/2024 0 Comments Itrace fresh![]() ( B) Modeled (purple) and observed ice core δ 18 O at Greenland Ice Sheet Project 2 (GISP2) (black) ( 13) and GRIP (gray) ( 49). ( A) Climate forcings including June solar insolation at 60°N (red), CO 2 concentration (green), meltwater forcing at the Northern Hemisphere (blue) and the Southern Hemisphere (orange). Water isotope–climate evolution during the last deglaciation. Here, combining climate proxies with transient isotope-enabled climate model simulations, we resolve this puzzle and suggest that the HS1 cooling did occur but was not recorded in ice core δ 18 O. This apparent lack of δ 18 O response over Greenland has led to the speculation that Greenland did not cool during HS1, implying a decoupling of the Arctic from hemispheric climate trends ( 16). 1E) ( 15) to Asian monsoon speleothem calcite isotope δ 18 O c ( Fig. ![]() 1, E and F) ( 9, 10), from North Atlantic sea surface temperature (SST) ( Fig. This is in contrast to other proxies across the Northern Hemisphere ( Fig. Here, we focus on the last Heinrich event, the HS1, a period of weakened AMOC from 18 to 14.7 ka before present (BP) ( 11), which contains the abrupt Heinrich event 1 ice-rafted debris layers around 16.2 ka BP ( 12), while Greenland δ 18 O shows virtually no depletion signal around the HS1 onset at ~18 ka BP ( Fig. These events occur coherently in Northern Hemisphere proxy records ( Fig. Northern Hemisphere climate during the last deglaciation was punctuated by abrupt events such as Heinrich Stadial 1, Bølling-Allerød warming (BA 14.7 to 12.9 ka), and Younger Dryas cooling (YD 12.9 to 11.7 ka). These contrasting observations raise a fundamental question: Was Greenland climate not affected by Heinrich variability, or was Heinrich variability not recorded in Greenland δ 18 O? Consequently, the commonly used Greenland event stratigraphy ( 8) only identifies DO stadial-interstadial transitions but not Heinrich stadials. This contrasts proxies for Atlantic circulation and temperature ( 5, 6) and Asian monsoon ( 7) that show clearly distinct signatures of the Heinrich stadials. However, Greenland δ 18 O fails to differentiate the DO and Heinrich stadials from similar δ 18 O levels in Heinrich stadials and regular DO stadials. Greenland ice core δ 18 O of water isotopes is a commonly used proxy for site temperature due to the “temperature effect” ( 4) and has been considered as a key index that records abrupt climate changes around the Arctic region. Heinrich stadials are generally believed to represent more-complete AMOC shutdown and, thus, more-extreme winter cooling than DO stadials ( 3). Glacial periods exhibit Dansgaard-Oeschger (DO) and Heinrich modes of abrupt climate variability, both of which are linked to changes in Atlantic meridional overturning circulation (AMOC) ( 1, 2). Our work suggests that Greenland δ 18 O may substantially underestimate temperature variability during cold glacial conditions. In contrast, the Arctic summer warmed during HS1 and YD because of increased insolation and greenhouse gases, consistent with snowline reconstructions. However, this cooling signal in the depleted oxygen isotopic composition is completely compensated by the enrichment because of the loss of winter precipitation in response to sea ice expansion associated with AMOC slowdown during extreme glacial climate. Here, combining proxy records with an isotope-enabled transient deglacial simulation, we propose that a substantial HS1 cooling onset did indeed occur over the Arctic in winter. However, one long-standing puzzle is the apparent absence of the onset of the Heinrich Stadial 1 (HS1) cold event around 18 ka in Greenland ice core oxygen isotope δ 18 O records, inconsistent with other proxies. Abrupt climate changes during the last deglaciation have been well preserved in proxy records across the globe.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |