Testing Massive Arctic Sea Ice Export as a Trigger for Abrupt Climate Change

Abstract:

The discharge of large volumes of freshwater from glacial lakes to the subpolar North Atlantic is repeatedly cited as one of the main triggers for abrupt centennial-to-millennial length climate cooling during the last deglaciation. Here we investigate an alternative mechanism focusing on whether the break-up and mobilization of thick, multiyear, Arctic sea ice – so called ‘paleocrystic’ sea ice – might have supplied enough freshwater to the Nordic Seas to reduce North Atlantic Deep Water (NADW) formation and weaken the AMOC. Indeed, low biological productivity and extremely low, or absent, sediment deposition in the Arctic during glacial periods suggest that parts of the central and western Arctic Ocean were covered by very thick, perennial ice.

Here we use a numerical climate model to assess: (1) whether paleocrystic ice covered much of the Arctic Ocean during glacial periods, (2) the mechanisms leading to the collapse and mobilization of Arctic sea-ice into the North Atlantic, and (3) the impact of melting sea ice on global ocean circulation. Preliminary results suggest that Arctic sea ice grows up to ~24 – 54 meters in LGM-type conditions and that the Arctic Ocean north of Fram Strait can store ~1.4 – 2.9x10¹⁴ m³ of freshwater as ice. If this ice was released from the Arctic in 1yr (10yrs) it would have been equivalent to a high-latitude freshwater forcing of 3–6 Sv (0.3–0.6 Sv), which is comparable (or larger) in magnitude than most estimates of meltwater emanating from glacial Lake Agassiz believed to have triggered episodes of dramatic global cooling during the last deglaciation.