Modelling North Atlantic's Heinrich events and associated impacts on the Earth System
Lead Research Organisation:
University of Bristol
Department Name: Geographical Sciences
Abstract
Future climate change involves complex interactions between physical processes on land, in the ocean, in the cryosphere, and in the atmosphere. Moreover, by all natural standards the changes predicted over the next century are likely to be 'rapid'. To have confidence in the predictions of models for the future behaviour of the ice-ocean-atmosphere-biosphere system, it is valuable for models to be tested and evaluated against past rapid Earth System changes. Although there are no direct analogues for future change, past rapid events allow us to investigate the ability of models to simulate the processes, feedbacks and time scales of response. Past climate behaviour is recorded within ice cores, marine sediment cores, cave and lake deposits and in geomorphological land forms. From these data there are clear climate cycles both on long time scales (glacial to interglacial, 100 kyr) and more rapid variations on millennial time scales (1.5 kyr - 16 kyr periods). One type of rapid variation is the massive release of icebergs from the ice sheets surrounding the North Atlantic, as indicated by freshening of the water column and increased deposition of Ice Rafted Debris (IRD) within marine sediment cores (Heinrich events). The Earth system response to these rapid changes are nearly instantaneous, with near synchronous changes in air temperature identified from ice cores in Greenland, emphasizing the sensitivity of the climate to freshwater forcing in the North Atlantic. Further feedbacks are observed through changes in vegetation, indicating changes in not only temperature but also in precipitation. Advances of glaciers across the globe at these times support a global cooling signal. While enhanced upwelling along the West coast of Africa points towards an increase in the strength of the South Atlantic trade winds. While these data tell us the timing and spatial pattern of Earth system changes associated with Heinrich events, numerical models are required to quantify the important processes related to these short term climate oscillations. Numerical modelling has already been used to reveal the importance of freshening of the North Atlantic to global climate, however, a number of aspects of these Heinrich events remain largely unexplained. Firstly, the mechanism for the trigger of ice sheet surging that produces the large number of icebergs. Secondly, the mode within which sediment is transported by the icebergs over the large distances observed within the marine records. Thirdly, the feedbacks and teleconnections which exist within the climate system that produces the wealth of evidence of both synchronous and asynchronous global signals associated with these events. This project aims to address these issues by using a newly developed fully coupled GCM which includes a detailed fully dynamic atmosphere-ocean model, combined with an ice sheet model, a vegetation model and a carbon cycle model. The model includes isotopic representation and can be coupled offline to dust and methane emission models. The model will be used to investigate the mechanisms and timings associated with the Heinrich events and associated Earth system changes. Understanding these processes and feedbacks within the Earth system and being able to compare the modelled results to the data of these past climatic events will give us confidence in using these models to predict future responses of the Earth system.
Publications
Huntley B
(2013)
Millennial climatic fluctuations are key to the structure of last glacial ecosystems.
in PloS one
Roberts W
(2014)
A new constraint on the size of Heinrich Events from an iceberg/sediment model
in Earth and Planetary Science Letters
Roberts W
(2014)
ENSO in the Mid-Holocene according to CSM and HadCM3
in Journal of Climate
Roberts WH
(2014)
Topography's crucial role in Heinrich Events.
in Proceedings of the National Academy of Sciences of the United States of America
Gregoire L
(2015)
The relative contribution of orbital forcing and greenhouse gases to the North American deglaciation
in Geophysical Research Letters
Roberts W
(2016)
The role of basal hydrology in the surging of the Laurentide Ice Sheet
in Climate of the Past
Gregoire LJ
(2016)
Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise.
in Geophysical research letters
Valdes P
(2017)
Green Mountains and White Plains: The Effect of Northern Hemisphere Ice Sheets on the Global Energy Budget
in Journal of Climate
Description | The major goal of the project was to simulate the complete evolution of a Heinrich Event using a fully coupled Earth System Model: this was accomplished. We developed the ice sheet model to simulate ice sheet surges (Objective 1) and used this to simulate the complete evolution of a Heinrich Event (Objective 2). Further experiments indicated that understanding isopycnal flows from the ice sheet were not important (Objective 3). Under the broad Objectives 4 and 5, to understand the impact of Heinrich Events on the broader climate system, we undertook a suite of sensitivity tests using the model to understand how the ocean and atmospheric forcing from the ice sheet can impact the climate. The results from this part of the project are likely the strongest legacy. We showed that the atmospheric forcing from the ice sheet is as important as the ocean forcing, overturning the current paradigm that the global impacts of Heinrich Events are felt through the ocean. |
Exploitation Route | The important role that the interactions between the atmosphere and ice sheet can play is being actively pursued in the context of how the climate varies over a glacial cycle, not just during the unique Heinrich Events. This is an important consideration for the whole climate dynamics community. Similarly the palaeo-data community are actively now considering how to interpret their records in the context of changes to the atmospheric circulation. The modelling framework of a coupled climate/ice sheet model is being actively developed to include a more sophisticated interface between the climate model and the ice sheet model and a more advanced ice sheet model. This development is being done in colloboration with the UKESM community and puts the UK at the forefront of the climate/ice sheet modelling community. Understanding the dynamic changes that can occur in ice sheets can be extended to other times during the ice ages. We are pursuing the idea that large ice sheets can naturally ebb and flow during an ice age to understand better the evolution of the whole ice sheet. This is work with geomorphologists who can track past regions of active ice movement. |
Sectors | Energy Environment |
Description | Constraining the size of Heinrich Events using and iceberg sediment model |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Study participants or study members |
Results and Impact | QRA Workshop "Heinrich Events: Land, Ice and Ocean", Southampton, U.K. (2012) |
Year(s) Of Engagement Activity | 2012 |
Description | Constraining the size of Heinrich Events using and iceberg/sediment model and a 3D ice sheet mode |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other audiences |
Results and Impact | Conference talk at 22nd V.M. Goldschmidt Conference, Montreal Canada, 2012 |
Year(s) Of Engagement Activity | 2012 |
Description | The tropical Pacific climate response to the changing forcing over the last glacial cycle |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other audiences |
Results and Impact | 4th PAGES OSM, Goa, India (2013) |
Year(s) Of Engagement Activity | 2013 |