Periodic fluctuations in deep water formation due to sea ice

TL;DR

This paper presents a simple dynamical model linking sea ice and ocean circulation to explain the periodicity and burst patterns of Dansgaard-Oeschger events during the last ice age, highlighting sea ice's insulating role.

Contribution

It introduces a novel dynamical model demonstrating how sea ice interactions can produce self-sustained oscillations and explain the timing of past climate events.

Findings

Sea ice causes periodic heat venting from the deep ocean.

Freshwater forcing modulates the natural oscillation, creating burst patterns.

The 1,500-year cycle is linked to ocean geometry and heat capacity.

Abstract

During the last ice age several quasi-periodic abrupt warming events took place. Known as Dansgaard-Oeschger (DO) events their effects were felt globally, although the North Atlantic experienced the largest temperature anomalies. Paleoclimate data shows that the fluctuations often occurred right after massive glacial meltwater releases in the North Atlantic and in bursts of three or four with progressively decreasing strengths. In this study a simple dynamical model of an overturning circulation and sea ice is developed with the goal of understanding the fundamental mechanisms that could have caused the DO events. Interaction between sea ice and the overturning circulation in the model produces self-sustained oscillations. Analysis and numerical experiments reveal that the insulating effect of sea ice causes the ocean to periodically vent out accumulated heat in the deep ocean into the atmosphere. Subjecting the model to idealized freshwater forcing mimicking Heinrich events causes modulation of the natural periodicity and produces burst patterns very similar to what is observed in temperature proxy data. Numerical experiments with the model also suggests that the characteristic period of 1,500 years is due to the geometry, or the effective heat capacity, of the ocean that comes under sea ice cover.