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Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective

Abstract

This study analyzes a three-member ensemble of experiments, in which 0.1 Sv of freshwater was applied to the North Atlantic for 100 years in order to address the potential for large freshwater inputs in the North Atlantic to drive abrupt climate change. The model used is the GFDL R30 coupled ocean-atmosphere general circulation model. We focus in particular on the effects of this forcing on the tropical Atlantic region, which has been studied extensively by paleoclimatologists. In response to the freshwater forcing, North Atlantic meridional overturning circulation is reduced to roughly 40% by the end of the 100 year freshwater pulse. Consequently, the North Atlantic region cools by up to 8 C. The extreme cooling of the North Atlantic increases the pole-to-equator temperature gradient and requires more heat be provided to the high latitude Atlantic from the tropical Atlantic. To accommodate the increased heat requirement, the ITCZ shifts southward to allow for greater heat transport across the equator. Accompanying this southward ITCZ shift, the Northeast trade winds strengthen and precipitation patterns throughout the tropical Atlantic are altered. Specifically, precipitation in Northeast Brazil increases, and precipitation in Africa decreases slightly. In addition, we find that surface air temperatures warm over the  More>>
Authors:
Dahl, Kristina A; [1]  Broccoli, Anthony J; [2]  Stouffer, Ronald J [3] 
  1. Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program, Woods Hole, MA (United States)
  2. Rutgers University, Department of Environmental Sciences, New Brunswick, NJ (United States)
  3. Geophysical Fluid Dynamics Laboratory, Princeton, NJ (United States)
Publication Date:
Mar 01, 2005
Product Type:
Journal Article
Resource Relation:
Journal Name: Climate Dynamics; Journal Volume: 24; Journal Issue: 4; Other Information: PBD: Mar 2005
Subject:
58 GEOSCIENCES; CLIMATIC CHANGE; GENERAL CIRCULATION MODELS; OCEANIC CIRCULATION; WATER CURRENTS; NORTHERN HEMISPHERE; ATLANTIC OCEAN; RESPONSE FUNCTIONS; COMPUTERIZED SIMULATION
OSTI ID:
20589702
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
Journal ID: ISSN 0930-7575; CLDYEM; TRN: DE05G4644
Availability:
Available from: http://dx.doi.org/10.1007/s00382-004-0499-5
Submitting Site:
DE
Size:
page(s) 325-346
Announcement Date:
Jun 12, 2005

Citation Formats

Dahl, Kristina A, Broccoli, Anthony J, and Stouffer, Ronald J. Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective. Germany: N. p., 2005. Web. doi:10.1007/s00382-004-0499-5.
Dahl, Kristina A, Broccoli, Anthony J, & Stouffer, Ronald J. Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective. Germany. doi:10.1007/s00382-004-0499-5.
Dahl, Kristina A, Broccoli, Anthony J, and Stouffer, Ronald J. 2005. "Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective." Germany. doi:10.1007/s00382-004-0499-5. https://www.osti.gov/servlets/purl/10.1007/s00382-004-0499-5.
@misc{etde_20589702,
title = {Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective}
author = {Dahl, Kristina A, Broccoli, Anthony J, and Stouffer, Ronald J}
abstractNote = {This study analyzes a three-member ensemble of experiments, in which 0.1 Sv of freshwater was applied to the North Atlantic for 100 years in order to address the potential for large freshwater inputs in the North Atlantic to drive abrupt climate change. The model used is the GFDL R30 coupled ocean-atmosphere general circulation model. We focus in particular on the effects of this forcing on the tropical Atlantic region, which has been studied extensively by paleoclimatologists. In response to the freshwater forcing, North Atlantic meridional overturning circulation is reduced to roughly 40% by the end of the 100 year freshwater pulse. Consequently, the North Atlantic region cools by up to 8 C. The extreme cooling of the North Atlantic increases the pole-to-equator temperature gradient and requires more heat be provided to the high latitude Atlantic from the tropical Atlantic. To accommodate the increased heat requirement, the ITCZ shifts southward to allow for greater heat transport across the equator. Accompanying this southward ITCZ shift, the Northeast trade winds strengthen and precipitation patterns throughout the tropical Atlantic are altered. Specifically, precipitation in Northeast Brazil increases, and precipitation in Africa decreases slightly. In addition, we find that surface air temperatures warm over the tropical Atlantic and over Africa, but cool over northern South America. Sea-surface temperatures in the tropical Atlantic warm slightly with larger warm anomalies developing in the thermocline. These responses are robust for each member of the ensemble, and have now been identified by a number of freshwater forcing studies using coupled OAGCMs. The model responses to freshwater forcing are generally smaller in magnitude, but have the same direction, as paleoclimate data from the Younger Dryas suggest. In certain cases, however, the model responses and the paleoclimate data directly contradict one another. Discrepancies between the model simulations and the paleoclimate data could be due to a number of factors, including inaccuracies in the freshwater forcing, inappropriate boundary conditions, and uncertainties in the interpretation of the paleoclimate data. Despite these discrepancies, it is clear from our results that abrupt climate changes in the high latitude North Atlantic have the potential to significantly impact tropical climate. This warrants further model experimentation into the role of freshwater forcing in driving climate change. (orig.)}
doi = {10.1007/s00382-004-0499-5}
journal = {Climate Dynamics}
issue = {4}
volume = {24}
journal type = {AC}
place = {Germany}
year = {2005}
month = {Mar}
}