HISTORICAL OBSERVATIONS OF COASTAL UPWELLINGS ALONG THE NORTHERNBEACHES OF THE NORTH CAROLINA OUTER BANKS*

摘要

Coastal upwelling occurs when coast-parallel winds drive surface waters offshore causing cold, nutrientrich, water to displace warm surface water. If seasonally persistent, these events and their associatedblooms of microorganisms can ultimately lead to a transient enrichment of local marine life, but also havethe potential to produce subsequent depressed levels of dissolved oxygen due to increased rates of organicconsumption and decay. The anoxic conditions thus created can be very harmful to indigenous benthicbiota. This study examines sea surface temperature image data to determine the presence of upwellingevents along the coastline of North Carolina, specifically at Cape Hatteras and Duck Pier, and establishescorrelation with archived wind data and topographic highs as revealed by the most current NOAAHydrographic charts of the two locations. The wind direction and average wind speed were found to begood indicators of upwelling events; although, wind direction was found to have greater influence on theoccurrence of coastal upwelling. The portion of the North Carolina coast, from Cape Hatteras to DuckPier, is oriented slightly southeast to northwest; therefore, coastal upwelling were driven by seasonalwinds out of the South to Southeast. There exist a highly significant correlation between upwelling eventsand persistent wind direction as well as with topographic highs, which are means to alert marineauthorities, marine agricultural interests, and the public to the possible risk of anoxic events which mightdo considerable harm to the local shell or sport fishing industry.Level-three sea surface temperature image data for Cape Hatteras and Duck Pier were obtained from theAdvanced Very High Resolution Radiometer (AVHRR) on board the NOAA-12, 15, 16, and 17 orbitingsatellites. Lview Pro image processing software was used to determine the sea surface temperatureapproximately three kilometers East of Cape Hatteras and Duck Pier by matching the RGB color valuesof those points on the image to the RGB color values on the imagea€?s temperature scale. Sea surfacetemperature data for Cape Hatteras and Duck Pier were also obtained from the National Data Buoy Center(NDBC) at Station 41025 and Station DUCN7, respectively. Water temperature data for Duck Pier wereobtained from the Field Research Facility (FRF). These data were computed from 6 temperature sensorsmounted at the End-of-Pier (EOP) in nominal water depths of 1, 2, 3, 4, 5, and 7 meters. Although theNOAA AVHRR sea surface temperature data was used as the primary source, additional sea surfacetemperature data were obtained to verify accuracy.Daily wind direction and average wind speed data for Cape Hatteras and Duck Pier were obtained fromNOAA National Weather Service (NWS). Wind data for the two locations were also obtained fromNDBC. The focus of this study is the months of June, July, and the first fifteen days of August of 2000.Wind data were used to establish correlation between persistent wind direction and upwelling events bysupporting or repudiating alleged upwelling events that were solely based on sea surface temperaturedata. The duration, sea surface temperature, and wind data were recorded for each upwelling event.Finally, topographic data were obtained for Cape Hatteras and Duck Pier from NOAA Bathymetry charts#11555 and #12204, respectively. Bathymetry charts were analyzed for ridge-lines and topographichighs.