Characterization of the Gulf Stream in transient CMIP6 scenarios

CMIP6 Hackathon CMIP6 Project Proposals
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Your Project Title

Characterization of the Gulf Stream in transient CMIP6 scenarios

Scientific Motivation

The Gulf Stream is a western boundary current that transports heat, salt, and oxygen-poor, nutrient-rich waters poleward. As the northward flowing upper limb of the Atlantic Meridional Overturning Circulation (AMOC), it plays a major role in climate variability (e.g. Palter 2015). Additionally, it influences sea level in the mid-Atlantic coast (Ezer et al. 2017) and also North Atlantic biogeochemistry. For example, the Gulf Stream drives uptake of atmospheric CO2 as subtropical waters cool along its path (Takahashi et al. 2002), supplies nutrients to the oligotrophic gyres via cross-front transport (Yamamoto et al. 2018), and affects the oxygen inventory (Tagklis et al. 2017). Therefore, understanding how the Gulf Stream will evolve in a warming ocean is crucial to predict the evolution of the climate, ocean circulation, and ocean biogeochemistry in the Atlantic Ocean.

A poleward shift of the Gulf Stream over the past century has been seen in surface observations and reanalysis products (Wu et al. 2012). This ongoing shift has been linked to dramatic warming and deoxygenation in the northwest Atlantic shelf in response to transient CO2 emissions (Saba et al. 2015, Claret et al. 2018). Moreover, this poleward shift is associated with a spatial pattern in sea surface temperatures of cooling in the subpolar North Atlantic and warming on the Scotian Shelf, which has been suggested as a fingerprint of the AMOC slowdown (Caesar et al. 2018). While these works are canaries in the climate change coal mine, much remains unknown about the variety of phenomena driving the observed shift or its large-scale impacts.

Proposed Hacking

This project aims to characterize the Gulf Stream in CMIP6 scenarios of transient CO2 emissions. Analyses carried out within this project will aim to explore the following potential questions:

  • Where does the Gulf Stream separate from the US coast in CMIP6 models? Coarse-resolution models (e.g. 1deg) are known to have a warm bias in the northwest Atlantic shelf, since the Gulf Stream separates too far north of Cape Hatteras (Saba et al. 2015). Assessing this potential bias in control simulations will help us interpret potential changes in the Gulf Stream in transient CO2 emission scenarios.

  • Will the Gulf Stream strength also change in a changing climate? Does its stability increase with ocean warming? If, so, would this have an impact on the cross-front transport of nutrients?

  • Is an ocean-atmosphere coupled model necessary to simulate a poleward shift of the Gulf Stream? In other words, do ocean-atmosphere feedbacks play a role on determining long-term shifts in the Gulf Stream position and/or strength?

Anticipated Data Needs

Sea level height, potential temperature, salinity, and oxygen for transient CO2 emission scenarios. Models with an ocean resolution of ¼ deg or higher.

Anticipated Software Tools

Fairly new to python so any suggestion is very welcome.

Desired Collaborators

Curious and motivated minds.

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