North Pacific

Overview

Some of the most dramatic changes in climate over the last glacial and deglacial period were associated with changing deep water formation. Deep water formation in the North Atlantic today helps transport heat northwards, warming Britain and Northern Europe. Abrupt changes in this “conveyor belt” circulation in the past are thought to have driven rapid climate changes of more than 10 C in a decade during the last glacial period. Deep water formation in the Southern Ocean helps control CO₂transfer between the vast reservoir of carbon in the deep ocean and CO₂in the atmosphere, and changes in this deep circulation may drive changes in atmospheric CO₂both past and future.

The North Pacific has been largely overlooked in consideration of climate and CO₂change, due to the lack of deep water formation in this region. Today, the North Pacific is stratified by low salinity waters ponded on this basin’s surface, and it has been largely assumed that this state is not liable to change.

However during the last deglaciation, new geochemical data suggests that a burst of North Pacific deep water formation took place, likely driven by an abrupt reduction in rainfall. Work with a biogeochemical model shows that this likely released CO₂stored in the deep ocean into the atmosphere, which may have helped end the last ice age. This discovery radically alters models for the last deglaciation, and represents a hitherto unrealized mode of climate variability.

Although the implications of deep water formation in the North Pacific are profound, research on this process is in its infancy. For instance evidence for deep water formation currently rests on results from a single sediment core, limiting confidence in the robustness of this signal and providing no information on its spatial extentJust as the discovery of switches in North Atlantic deep water formation prompted study of whether modern climate change might turn off this circulation and its attendant heat transport, knowledge that North Pacific deep water formation can turn on and release vast quantities of CO₂from the ocean’s deep merits further study.

This project aims to transform knowledge of the North Pacific’s role in CO₂and climate change. We will use geochemical measurements of boron isotopes in microfossil shells (which record the behaviour of CO₂in seawater) and radiocarbon (which records how recently deep waters left the surface ocean) to test the extent of deep water formation in the North Pacific and its effect on CO₂rise. Our previous modelling predicts different signals for local versus distal deep water formation that should be recorded in the North Pacific by these data. We will also use boron isotopes to constrain CO₂storage in the deep Pacific during the ice age. The North Pacific is touted as one of the most likely reservoirs for CO₂storage during glacial periods, so knowledge of the nature of this storage, and how it changed over the deglacial, is required to address the long-standing climate problem of glacial-interglacial CO₂change. The implications of these glacial and deglacial data will be quantitatively explored in an earth system model. The accuracy of these CO₂chemistry reconstructions will be aided by new calibrations for the relationship between boron isotopes and the CO₂system from recent samples.