Has the Gulf Stream Slowed or Shifted in the Altimetry Era?

Abstract

The Gulf Stream (GS) is expected to slow and shift poleward over the next century due to climate change. We investigate whether such changes are already observable in the altimetric record (1993–2018) using along-track altimetry. Decadal trends in latitude, speed, transport, and width are calculated in stream-following coordinates to avoid spurious signals due to changes in higher-frequency GS variability. Statistically significant trends are few and apparently randomly distributed. Further, small changes to the length of the record lead to large changes in the trends and their significance. These results suggest that the current observations are insufficient to detect significant trends in these metrics. If the trends continue at the current rate, detection of trends at more than half of the altimetry tracks would require 22–23 additional years of observations for latitude and transport and 44 additional years for speed.

Plain Language Summary

The Gulf Stream (GS) transports warm water into the high latitudes of the North Atlantic and is partially responsible for Europe's mild climate. It is expected to slow down and shift northward over the next century in response to climate change. This study investigates whether these trends are already detectable using satellite measurements of sea surface height. GS speed, width, and transport are calculated in coordinates which are always centered on the GS axis to avoid potential false trends from changes in the variability of the GS position. Few observed trends are statistically different from zero and small changes to the length of the record lead to large differences in the magnitude of the trends. This means that GS has too much short-term variability to reliably detect trends over the length of the satellite record (1993–2018). Additional observations may make it possible to detect trends. Assuming the GS's future variability is consistent with that over the observed record, we estimate that an additional 22–23 years of observations would be required to detect trends in latitude and transport, while detecting trends in speed would require 44 additional years.