3.1. Brown Bluff

SITE DESCRIPTION

Brown Bluff is an area situated on the northern-most tip of the Antarctic Peninsula, exposed to the Antarctic Sound. It consists of a 1.5 kilometer cobble beach, increasing steeply to high red-brown cliffs. There were large glaciers on either side of the beach that descended down from the continent and were in contact with the ocean. Conductivity-temperature-depth (CTD) sampling at Brown Bluff was done on the morning of February 20th, 2011 at five different stations. Looking at the figures below, it can be seen that station 1 was the farthest station away from the shore (1.2 km); stations 2 and 3 were approximately 500 meters away; station 4 was approximately 200 meters away; and station 5 and station 6 (seen on Figure 4 as station 6: station 5 and 6 represent repeated observations at one location) were approximately 600 meters away from shore. Most notably, station 4 was the closest to a glacier, and both station 3 and station 5/6 were situated next to an iceberg.

Figure 4: Location of the 5 stations at Brown Bluff

Figure 5 : Brown Bluff defined section

TEMPERATURE

The temperature at Brown Bluff did not vary greatly. For all the stations it remained between -0.52°C and -0.75°C (see figure 6), with the average temperature approximately -0.7°C. Stations 1, 2 and 4 had hardly any thermocline present, exhibiting a constant temperature of -0.68°C as depth increased (up to 17 meters below the surface). Station 3 had a slightly warmer temperature for the first 6 meters (-0.62°C), which can be seen in the section plot as a larger section of green present just below the surface, representing warmer temperatures. Afterward, the temperature decreased, forming a thermocline until reaching the average temperature at 8 meters below the surface. Station 6 had the warmest surface temperature of all the sites (-0.52°C), and the most pronounced thermocline. This warm water trend is seen in both the station and section plots in Figure 6, where it can also be seen that the coldest temperature was reached (-0.75°C) at 5 meters below the surface, where it then remained constant as depth decreased.

Table 2: Brown Bluff station locations and associated symbols

Figure 6.1: Temperature station plot for Brown Bluff Figure 6.2: Temperature section plot for Brown Bluff

SALINITY

Measurements at Brown Bluff demonstrate that salinity is more important in producing water stratification than the temperature. All the stations show fresher water near the surface and more saline water at deeper depths. Salinity of the different stations was also influenced by the incoming fresh water melting from the glaciers. Station 4 presented the greatest salinity range, from 34.1 to 34.3 psu (practical salinity units). It also exhibited a pronounced pycnocline in the first 3 meters below the surface. Station 3 presented a relatively constant salinity over the first 6 meters of depth (similar to temperature) before it entered into a pycnocline. Sites 1, 2 and 6 had increasing densities with depth, yet without a pronounced pycnocline. Looking at the section plot (see figure 7.2), the salinity stratification across the area is well illustrated. The glaciers’ location is also well indicated through the section with a thicker layer of fresher water, which corresponds to the pycnoclines in the water column.

Figure 7.1: Salinity station plot for Brown Bluff Figure 7.2 Salinity section plot for Brown Bluff

T/S PLOT

The potential temperature/salinity (T/S) plot (see figure 8) serves to demonstrate again how Brown Bluff was more salinity-stratified than temperature-stratified. In general, the stations had a greater range of salinity compared to the temperature range. The average potential density at Brown Bluff measured approximately 27.5kg/L. Station 4 was more salinity-stratified (it had the freshest water of all the sites at the water surface), and presented a large range in potential density with a relatively constant temperature. This correlates to its close location to onshore glaciers. The Station 3 data also presents a large change in density for the same reason. Our results show that Station 2 had the most constant density, as it had rather constant temperature and salinity.

Figure 8: T/S plot with isopycnals for Brown Bluff

DENSITY

Our density results from Brown Bluff (see figure 9) are relatively constant below a certain depth, with a density of around 17.5 kg/m3. In the first 8 meters, though, density variations can be observed. Station 2 had the most constant density with no pycnocline, which is consistent with the T/S plot (see figure 8). Stations presented a decrease in density, with the least dense water at its surface. This is also in agreement with station 4 having the freshest surface water. Station 3 had a density that varied around 6 meters, which was the same depth for this site’s thermocline and pycnocline. We can suggest interference with a different current at this depth. The section plot (see figure 9.2) also illustrates such a stratification in these different water layers. When looking at the section again, a deeper current around 18 meters also suggests the input of denser water from that current.

Figure 9.1: Density station plot for Brown Bluff Figure 9.2: Density section plot for Brown Bluff

SECCHI DEPTH

Overall, the productivity at Brown Bluff was fairly low at all the stations, evidenced by the deep Secchi Depth values which were observed: station 1 measured 10 meters, station 2 measured 12 meters, station 3 measured 13 meters, station 4 measured 15 meters, and station 6 measured 17.5 meters.