Decadal Changes in the World's Coastal Latitudinal Temperature Gradients

Area of Science:

• Marine ecology
• Climate science
• Oceanography

Background:

• Coastal environments host most marine life and exhibit predictable temperature changes with latitude.
• Coastal latitudinal temperature gradients (CLTG) are associated with ecological patterns, but their linkage is not fully understood.
• Characterizing global CLTGs is a crucial first step to understanding these connections.

Purpose of the Study:

• To quantify the spatial and temporal variability of the world's major coastal latitudinal temperature gradients (CLTG).
• To analyze changes in CLTG strength over the past three decades (1982-2012).
• To investigate the relationship between annual mean sea surface temperature (SST) trends and seasonality.

Main Methods:

• Extracted coastal cells from a global 1°×1° dataset of weekly sea surface temperatures (SST) from 1982-2012.
• Quantified CLTG strength using the slope of the linear mean-SST/latitude relationship.
• Analyzed annual and seasonal SST trends and changes in seasonality (summer-winter amplitude).

Main Results:

• CLTG strength varied significantly, with the steepest gradients on the North American Atlantic and Asian Pacific coasts and the weakest on the African Indian Ocean and South/North American Pacific coasts.
• Seven out of eleven major CLTGs have weakened by 3-10% over 31 years due to differential warming at high versus low latitudes.
• The South American Pacific coast has cooled, while the North American Atlantic gradient's weakening is due to high-latitude warming and mid-latitude cooling. Three-quarters of coastal cells showed increased seasonality.

Conclusions:

• Global climate change has a regionally variable impact on coastal marine environments.
• Changing CLTGs and increased seasonality are likely driving observed spatial and temporal patterns in coastal marine life.
• Understanding these thermal shifts is critical for predicting the ecological consequences for marine biodiversity.