Interannual variability in sea surface temperature and fCO₂ changes in the Cariaco Basin

We examined the variability of sea surface carbon dioxide fugacity (fCO₂ₛₑₐ) and its relation to temperature at the Cariaco Basin ocean time-series location (10°30′N, 64°40′W) for the period from 1996 through 2008. Periods of warm (positive) and cold (negative) anomalies at the station were related to variability in coastal upwelling intensity. A positive temporal trend in monthly-deseasonalized sea surface temperatures (SST) was observed, leading to an overall increase of 1.13°C over 13 years. Surface fCO₂ₛₑₐ displayed significant short-term variation (month to month) with a range of 330–445μatm. In addition to a large seasonal range (58±17μatm), deseasonalized fCO₂ₛₑₐ data showed an interannual positive trend of 1.77±0.43μatmyr⁻¹. In the Cariaco Basin, positive and negative anomalies of temperature and fCO₂ₛₑₐ are in phase. An increase/decrease of 1°C coincides with an increase/decrease of 16–20μatm of fCO₂ₛₑₐ. Deseasonalized fCO₂ₛₑₐ normalized to 26.05°C, the mean Cariaco SST, shows a lower rate of increase (0.51±0.49μatmyr⁻¹). Based on these observations, 72% of the increase in fCO₂ₛₑₐ in Cariaco Basin between 1996 and 2008 can be attributed to an increasing temperature trend of surface waters, making this the primary factor controlling fugacity at this location. During this period, a decrease in upwelling intensity was also observed. The phytoplankton community changed from large diatom-dominated blooms during upwelling in the late 1990's to blooms dominated by smaller cells in the first decade of the 21st century. The average net sea-air CO₂ flux over the study period is 2.0±2.6molCm⁻²yr⁻¹ employing the Wanninkhof parameterization, and 2.1±2.5molCm⁻²yr⁻¹ based on Nightingale's model. To further understand the connection between the changes observed in the Cariaco Basin, the relationships between interannual variability in the temperature anomaly with three modes of climate variability (AMO, NAO and ENSO) were examined. The correlations between SSTA and two of these climate modes (AMO and ENSO) only show very weak relationships, although they were significant.