Global patterns of change and variation in sea surface temperature and chlorophyll a

Piers K Dunstan,James Risbey,Alistair J Hobday,Didier Monselesan,Terence J O'Kane,Edward King,Peter A Thompson,Scott D Foster,Jason R Hartog

doi:10.1038/s41598-018-33057-y

Abstract

Changes over the scale of decades in oceanic environments present a range of challenges for management and utilisation of ocean resources. Here we investigate sources of global temporal variation in Sea Surface Temperature (SST) and Ocean Colour (Chl-a) and their co-variation, over a 14 year period using statistical methodologies that partition sources of variation into inter-annual and annual components and explicitly account for daily auto-correlation. The variation in SST shows bands of increasing variability with increasing latitude, while the analysis of annual variability in Chl-a shows mostly mid-latitude high variability bands. Covariation patterns of SST and Chl-a suggests several different mechanisms impacting Chl-a change and variance. Our high spatial resolution analysis indicates these are likely to be operating at relatively small spatial scales. There are large regions showing warming and rising of Chl-a, contrasting with regions that show warming and decreasing Chl-a. The covariation pattern in annual variation in SST and Chl-a reveals broad latitudinal bands. On smaller scales there are significant regional anomalies where upwellings are known to occur. Over decadal time scales both trend and variation in SST, Chl-a and their covariance is highly spatially heterogeneous, indicating that monitoring and resource management must be regionally appropriate.

Highlights

Understanding the spatial and temporal patterns of change in oceans is important for managing oceans by ensuring sustainable development and conservation[1,2]
We only consider time series for cells that have more than 25 observations over the study period, for each of Sea surface temperature (SST) and chlorophyll a (Chl-a), and we assume that missing data are randomly distributed in time
The interaction between annual variation in SST and Chl-a provides insights into how and where linkages occur on annual time scales

Summary

Introduction

Understanding the spatial and temporal patterns of change in oceans is important for managing oceans by ensuring sustainable development and conservation[1,2]. Understanding the observed spatial patterns, trends and variance of ocean states over these shorter time scales is important to complement other management, monitoring and planning efforts[5]. The patterns of temporal and spatial variability in Chl-a, and how it relates to temperature, directly link changes in climate with the dynamics of ocean ecosystems[1,3]. While the global average temperature is increasing[1], there is variability around this average with different regions and locations experiencing different responses, both in terms of the trend and variance on different time scales[5,8,9]. There is growing evidence that in some locations increasing wind speeds overcome any potential increase in stratification due to warming and produce increased Chl-a16,17 These processes in the oceans are, variable on multiple spatial and temporal scales with significant impacts on ecosystem dynamics[18]. We contrast patterns of variation between SST and Chl-a and show that the observed patterns of covariation between SST and Chl-a demonstrate both positive and negative relationships suggesting SST alone may not be a good predictor of changes in Chl-a at global scales

Methods

Results

Conclusion