3.3. Neko Harbour

SITE DESCRIPTION

Neko Harbour is located along the Danco Coast of the Antarctic Peninsula, just off of the Gerlache Strait (for a map of the area, see figure 19). We recorded our measurements in the harbour on the morning of February 22, 2011. The weather was overcast with thick, low-hanging clouds, which blocked out a great deal of sunlight; because Secchi Disk readings measure the depth to which light penetrates, the lack of direct sunlight likely affected our observations. The water was very calm, despite occasional calving activity present at the nearby glaciers. The calving ice shelf contributed to the large amount of ice covering the surface of the water, especially in close proximity to the shore. Additionally, as our measurements were taken relatively close to land - with the first reading only 300 meters offshore - the presence of a penguin rookery nearby may have also influenced the data which we gathered. Our first station, located at 62.537°W 64.848°S and about 300 meters offshore, was recorded at 8:18 AM. The water depth was approximately 37 meters. Our second station was recorded at 8:34 AM and was located at 62.537°W 64.847°S, slightly further from shore. Our third and final station was located at 62.536°W 64.846°S, the furthest station from shore, and was observed at 8:51 AM. We observed the water closest to the shore was slightly fresher and colder than the stations farther from shore, potentially due to the fact that surface ice decreased and distance from nearby glaciers increased from our first (closest to shore) to our final stations. Glacial runoff and melting of floating ice close to the shore likely played a role in producing the colder, fresher surface water at our first station.

Figure 19: Neko Harbour defined section

TEMPERATURE

The temperatures recorded at Neko Harbour show that the water was above 0°C at each of our stations and possessed a unique stratification in which temperature increased with depth (see figure 20). There was a noticeable amount of variation present in our casts as depth increased, with surface temperatures more than 0.5°C colder than the waters below in the case of the first station. The first station offered the largest thermocline, which was likely due to the greater amounts of ice that were present and covering the surface, causing surface temperatures to be lower there than further from shore. The ice floating on the surface thus had a clear effect on Neko Harbour’s water, as it caused surface waters to be fresh and their temperatures to remain near 0°C. The three stations all represented similar temperatures in their columns. The only noticeable features were that surface waters were colder the closer they were to shore, likely due to more surface ice and glacier effects, and that the third station had the warmest waters approaching the bottom of the cast. The warmest waters were present at the bottom of the CTD casts, and interestingly all three stations had approximately the same temperature at this depth.

Figure 20: Temperature station and section plots for Neko Harbour

SALINITY

The salinity stratification of Neko Harbour’s waters was predictable and very critical to the density stratification in the area. The first station closest to shore had the freshest surface waters, which was certainly due to the higher concentration of surface ice in this location as well as the influence from nearby glaciers. As we moved further from shore and the ice was comparatively less present on the surface, the salinity increased. The figure representing the Neko Harbour salinity section (figure 21) shows that the three stations were similarly stratified, yet salinity increases directly with distance from the shore. The critical importance that salinity possesses in Neko Harbour is that, because both temperature and salinity increased along with depth, salinity must therefore be the driving factor for density. Thus, salinity regulates the stratification in these waters.

Figure 21: Salinity station and section plots for Neko Harbour

Figure 22: Salinity section plot for Neko Harbour

T/S PLOT

The figure representing the potential temperature/salinity (T/S) plot (figure 23) illustrates that the stratification between the three stations in Neko Harbour were very similar. As depth increased, each cast showed that temperature and salinity increased closely across the stations. One notable difference was that the third station had some warmer waters near the bottom of the cast, which caused this data to deviate slightly from the pattern of the other two. The isopycnals shown on the potential density graph are nearly vertical, which is due to the fact that density is driven by salinity. This gives way to a less common stratification where cold water sits atop warmer water, which we noticed at each of the stations.

Figure 23: T/S plot with isopycnals for Neko Harbour

DENSITY

The Density Anomaly figure representing the data taken at Neko Harbour shows that density was similar at each of the three stations, yet there was a slight increase in density as we moved further from shore. This was likely caused by the greater concentration of surface ice closer to the shore, which would have had an effect on surface temperature, and an even greater effect on the salinity. Because the water was greater than 0°C, the ice was constantly melting on the water and making the waters fresher closer to shore. Thus, the effect of the surface ice on the water in Neko Harbour means that salinity is the driving factor for stratification and so density would in turn increase as we moved away from shore and surface ice was less present.

Figure 24: Density station and section plots for Neko Harbour

SECCHI DEPTH

Overall, Neko Harbour had fairly high productivity in its waters, as our Secchi Depth readings did not measure high. At 8:18 AM we recorded a Secchi depth reading of 10 meters at our first station, located at 62.537°W 64.848°S and about 300 meters offshore. Our second station was recorded at 8:34 AM and was located at 62.537°W 64.847°S, slightly further from shore, with the Secchi depth measuring 9 meters. Our third and furthest station from shore was located at 62.536°W 64.846°S and was observed at 8:51 AM; the Secchi depth was 8 meters. We thus concluded the trend that light penetration decreased farther from shore here.