Additional Abstracts .... Legendre, Louis Nixon, Scott Walker, Nan O'Donnell, James Hamilton, Peter Roman, Mike Hitchcock, Gary Rabalais, Nancy Report #19 Table of Contents

Alberto M. Mestas-Nunez¹ and David B. Enfield^2
1Cooperative Institute for Marine and Atmospheric Studies, Miami, FL
²NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, FL

Introduction:

Global and regional climatic signals as well as their effects in the Gulf of Mexico are discussed using Sea Surface Temperature (SST) as an indicator for climatic changes. Our main source of data are SST anomalies with respect to the long term seasonal cycle from the Kaplan reconstructed SST dataset for the period 1856-1991. First, we review the known global and regional climaticsignals present in the SST dataset and discuss (qualitatively) their influence on the climate of the Gulf of Mexico. Second, we focus on the Gulf itself and estimate which are the dominant effects there. Amongthe global and regional signals we have the El Nino-Southern Oscillation (ENSO) mode, the global warming, and the non-ENSO modes such as the Pacific Decadal Oscillation (PDO) related modes in the Pacific and the North Atlantic Oscillation (NAO) related multidecadal mode in the Atlantic.

By far the most dominant signal in the global climate system is the ENSO mode. The ENSO signal is well captured by the first complex Empirical Orthogonal Function of the global SST anomalies, which shows how the amplitude and phase of ENSO vary in space around the globe (Enfield and Mestas-Nunez, 1999a). We note, for example, that the warming in the Atlantic lags the warming in the NINO3 region by 1-3 seasons (3-9 months). We also note that the amplitude of the ENSO signal is very small in the Gulf of Mexico.

Global averages of the SST anomalies show that the oceans are warming and that the rate of warming is not uniform in space. The spatial distribution of the global warming signal can be estimated by differencing the temporally averaged SST anomaly time series for the second and first half of the record or alternatively by calculating the slope of a least-squares line at every grid point (Enfield and Mestas-Nunez 1999a). Both of these show that the global warming signal in the Gulf of Mexico is small.

To look at the decadal to multi-decadal variability we first removed the ENSO and the global warming signals from the SST anomaly records. Our analysis of the non-ENSO variability has revealed several modes of variability that correspond to known climatic signal described in the literature (Enfield and Mestas-Nunez 1999a, Mestas-Nunez and Enfield 1999c, Enfield and Mestas-Nunez 1999b). In the North Atlantic, the dominant signal is a multi-decadal mode that seems to be related to the NAO. In the Pacific, two modes of variability were found that seem to be related to the PDO. To investigate the importance of these modes in the Gulf of Mexico, we averaged the SST anomalies in the Gulf and correlated it with the non-ENSO modes of variability. This analysis shows that the Gulf of Mexico SST anomalies are significantly correlated with the North Pacific multi-decadal mode.

It is important to note that the fact that the ENSO and global warming signals are small in the average Gulf of Mexico SST anomalies does not mean that these components do not have an effect on the gulf's climate. ENSO and global warming can affect other variables in the global ocean-atmosphere system (e.g. precipitation, tropical storm activity) and those in turn affect the climate of the gulf. We conclude that further research of the oceanic and atmospheric variables is required to describe the climatic effects in the Gulf of Mexico. The apparent teleconnection with the PDO requires a closer look as well as its potential climatic impacts on the gulf's chemistry and biology.

Enfield, D.B. and A.M. Mestas-Nunez, 1999a. Multiscale variabilities in global sea surface temperatures and their relationships with tropospheric climate patterns. J. Climate, In Press.

Enfield, D.B. and A.M. Mestas-Nunez, 1999b. Inter-annual to multi-decadal climate variability and its relationship to global sea surface temperatures. Under review as a chapter In: Present and Past Inter-Hemispheric Climate Linkages in the Americas and their Societal Effects, V. Markgraf (Ed.), Cambridge Univ. Press.

Mestas-Nunex, A.M. and D.B. Enfield, 1999c. Rotated global modes of non-ENSO sea surface temperature variability. J. Climate, In Press.