Factors challenging our ability to detect long-term trends in ocean chlorophyll

[摘要] Global climate change is expected to affect the ocean's biologicalproductivity. The most comprehensive information available about the globaldistribution of contemporary ocean primary productivity is derived fromsatellite data. Large spatial patchiness and interannual to multidecadalvariability in chlorophyll a concentration challenges efforts to distinguisha global, secular trend given satellite records which are limited induration and continuity. The longest ocean color satellite record comes fromthe Sea-viewing Wide Field-of-view Sensor (SeaWiFS), which failed inDecember 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS)ocean color sensors are beyond their originally planned operationallifetime. Successful retrieval of a quality signal from the current VisibleInfrared Imager Radiometer Suite (VIIRS) instrument, or successful launch ofthe Ocean and Land Colour Instrument (OLCI) expected in 2014 will hopefullyextend the ocean color time series and increase the potential for detectingtrends in ocean productivity in the future. Alternatively, a potentialdiscontinuity in the time series of ocean chlorophyll a, introduced by achange of instrument without overlap and opportunity for cross-calibration,would make trend detection even more challenging. In this paper, wedemonstrate that there are a few regions with statistically significanttrends over the ten years of SeaWiFS data, but at a global scale the trendis not large enough to be distinguished from noise. We quantify the degreeto which red noise (autocorrelation) especially challenges trend detectionin these observational time series. We further demonstrate howdiscontinuities in the time series at various points would affect ourability to detect trends in ocean chlorophyll a. We highlight the importanceof maintaining continuous, climate-quality satellite data records forclimate-change detection and attribution studies.

[学科分类] 地球化学与岩石