AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 12: 15–25 (2002) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/aqc.496 An overview of the oceanography and Meteorology of the Falkland Islands J. UPTONa* and C.J. SHAWb a Fugro GEOS, Hargreaves Road, Swindon, UK b Shell International Exploration and Production, b.v. Volmerlaan 8, PO Box 60, 2280 AB Rijswijk, Netherlands ABSTRACT 1. This paper describes an overview of the oceanography and meteorology of the Patagonian Shelf and Falkland Islands, derived from reference material and a 16 month measurement program carried out on behalf of the Falklands Operators Sharing Agreement (FOSA) between June 1997 and October 1998. It was not intended that the referenced information in this presentation be exhaustive, the bias has been placed on describing the measurement survey. 2. Due to commercial confidentiality, presentations of data measured during the survey have been limited to time series and statistics. However, the confidentiality of the data does not necessarily preclude use of the data for future research purposes. 3. The analysis of current, tide, wave, wind and meteorological data is described and the nature of mechanisms driving the current and wave regime are suggested. 4. Offshore oceanographic measurements were carried out at three locations prior to a drilling programme by the semi-submersible drilling rig Borgny Dolphin and on board whilst drilling. Meteorological measurements were performed at two locations on the Islands and on the Borgny Dolphin. Drifting buoys were deployed and conductivity, temperature and depth (CTD) measurements were carried out to determine the position and intra-annual variation of the Falklands Current in the North Falklands Basin. 5. The primary oceanographic current flow features of this area are the Brazil and Falklands Currents, which meet at a confluence off the coasts of Argentina and Uruguay. The position of the front varies between approximately 30 and 408S, depending on changes in the relative strength of the two current systems. Current flows are stronger on the slope than on the Continental Shelf and are less tidally dominated. Although it is thought that the FOSA mooring locations were influenced by the margins of the Falklands Current, stronger flows have been reported to the north of the measurement location. Typical maximum recorded near-surface currents reached 0.8 msÀ1, with near-bed maxima reaching 0.55 msÀ1. 6. The wave climate was primarily driven by locally derived storms, resulting in events of short duration. Typical maximum significant wave heights of 8.9 and 9.4 m were recorded to the north and south of the Islands, respectively. Copyright # 2002 John Wiley & Sons, Ltd. KEY WORDS: oceanography; meteorology; currents; waves; temperature; Falklands Current; Brazil Current; conductivity; forecast *Correspondence to: J. Upton. Fugro Geos, Hargreaves Road, Swindon, SN25 5AL, UK. Copyright # 2002 John Wiley & Sons, Ltd. Received 9 August 2000 Accepted 19 June 2001 16 J. UPTON AND C. J. SHAW INTRODUCTION This paper describes an overview of the oceanography and meteorology of the Patagonian Shelf and Falkland Islands. It is considered that the scope of the paper should not include a detailed interpretation of the results or forcing mechanisms, which may be more appropriate for an oceanographic journal. Information has been derived from reference material and a 16 month measurement program carried out in the North Falklands Basin on behalf of the Falklands Operators Sharing Agreement (FOSA) between June 1997 and October 1998. Due to commercial confidentiality, presentations of data measured during the survey have been limited to time series and statistics. However, the confidentiality of the data does not necessarily preclude use of the data for future research purposes. Offshore oceanographic measurements were carried out at three locations prior to a drilling programme by the semi-submersible drilling rig Borgny Dolphin and on board whilst drilling. Meteorological data were recorded at three locations on the Islands and on the Borgny Dolphin. Drifting buoys were deployed and conductivity, temperature and depth (CTD) measurements were carried out to determine the position and intra-annual variation of the Falklands Current in the North Falklands Basin. Prior to this survey, measured data in the Patagonian Shelf area were concentrated to the north and south of the Falkland Islands, including studies such as the Deep Basin Experiment between 1993 and 1995 (Harkema and Weatherly, 1996) and bottom pressure recording experiments in Drake Passage (Vassie et al., 1998). Measurements of current and water properties have also been taken during the regular transit of research vessels to and from Antarctica. Widely available satellite data have been utilized in more recent years by researchers such as de Souza and Robinson (1998) for observation of Southwestern Atlantic oceanography. The FOSA measurement survey has provided a significant contribution to oceanographic information in the area. BACKGROUND OCEANOGRAPHY OF THE PATAGONIAN SHELF AND FALKLANDS BASIN Historically, there has been limited investigation of the oceanography of the Patagonian Shelf around the Falklands Basin. Measurements within the Falkland’s Current have been limited, although Saunders and King (1995) have presented results of two measurement transects across the Falklands Current. Primary topics of research in the area have concentrated on the large scale water mass movements and their interaction with bottom topography, coastal morphology and eachother, as well as bottom flow patterns concerning the fate of cooler water masses produced in the Southern Ocean. Within the area of interest, there are two distinct regions of bathymetry affecting large-scale water mass movements. The first is the Patagonian Shelf, extending over 300 km from the South American coastline, with the Falkland Islands situated on an eastward extension at the southern extent of the shelf. The second region is the Falklands Basin, comprising a steep-sided shelf break to the east and south of the Islands (Plate 1), combined with bottom features associated with energetic currents such as steep sided troughs, transient mud waves and scouring at the seabed. Two large-scale water masses affect the area; the first being a branch of the Atlantic South Equatorial Current that forms the Brazil Current (BC). The BC is a western boundary current flowing southwards from near the equator from Cape St. Roque, Brazil, to about latitude 30–408 S, and extending over the region of the shelf plateau. This current is warm and saline, being made up of subtropical water, with typical temperature and salinity values of around 198C and 36PSU, respectively (Piccolo, 1998). The second major water mass to affect the region is the Falklands Current (FC), which comprises cooler Sub-Antarctic Water and has a typical temperature of 78C and relatively low salinity of 33.5PSU. This current originates as a branch of the Antarctic Circumpolar Current (ACC) and flows eastward through Copyright # 2002 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 12: 15–25 (2002) FALKLAND ISLANDS OCEANOGRAPHY AND METEOROLOGY 17 Noaa Satellite UK Datawell Directional Waverider Buoy SEA SURFACE 120m 25m 2 Rubber Cords Sub-Surface Buoy 300 kHz WH ADCP with Flotation Collar and Argos Beacon Sub-Surface Buoyancy 490m Aanderaa RCM7 Current Meter 200m Aanderaa RCM7 Current Meter 100m 465m Aanderaa RCM7 Sonardyne Acoustic Current Meter Release 10m Sonardyne Acoustic Release and Aanderaa WLR7 Tide Gauge Ballast Weight Ballast Weight SEABED NOT TO SCALE Figure 1. Mooring deployment diagrams. Drake Passage before flowing round the shelf break to the east of the Falklands and northwards along the shelf edge off South America. These two water masses meet at a confluence region situated off the Argentina and Uruguay coast, extending between 30 and 508S, and as far offshore as 458W (Provost et al., 1992; Gordon, 1989; Garzoli Copyright # 2002 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 12: 15–25 (2002) 18 J. UPTON AND C. J. SHAW and Giulivi, 1994). The actual location of the confluence is dependent upon annual variability in the BC, which results from variability in the wind forcing of the South Atlantic gyre system, and to a lesser extent, semi-annual variability in the FC, which is forced by Southern Ocean flow changes. During the Austral summer, the confluence region is situated at its southern extreme and in winter (June–August) is situated at its northern extreme. Geostrophic currents in the region of the confluence are of the order of 1 msÀ1, with energetic shear and mixing in the frontal zone (Piccolo, 1998). The primary forcing mechanisms in the region are attributable to tide, wind and balance between Coriolis and pressure gradient forces, with density driven mechanisms having a lesser influence. Depth- averaged density driven currents have been reported to be of the order of 0.02–0.07 msÀ1 (Forbes and Garraffo, 1988). Geostrophic currents (primarily the Brazil and Falklands Currents) contribute the most significant forcing mechanism in terms of current speed and mass water transport. The presence of the FC raises the sea level over the whole Patagonian Shelf by around 0.65 m, forming the pressure gradient that maintains the FC (Glorioso and Flather, 1995). Flow velocities of the FC north of the Islands, obtained by model output (Glorioso and Flather, 1995), give maximum values due to geostrophic balance of 0.27 msÀ1, although surface currents have been shown to be up to 0.40 msÀ1 (Peterson, 1992). In the northern extent of the FC, where flow begins to move onto the shelf (around 35–408S), maximum current speeds are around 1.5 msÀ1 (Glorioso and Flather, 1995). South of the Falklands, the bathymetry of the seabed, particularly the Burdwood Bank and Falklands Trough, have significant effects on current flows. Gloriso and Flather’s model (1995) generated the strongest flows in the FC to the south of the Islands, around the Burdwood Bank.