The Drake Passage was much rougher on return but we have made it safely back to port in the Strait of Magellan. Since you last heard from the science crew aboard the LMG we have completed many scientific objectives. Our sleep deprived group worked around the clock until we began our voyage back to Punta Arenas on October 26. We completed 5 CTD casts, did one field installation and extracted more sediment cores, most notably JPC-8, KC-7B and JKC-15.
A CTD cast consists of dropping a large rosette with 24 ten liter sample bottles and a multitude of sensors into the ocean. The nomenclature CTD is derived from Conductivity and Temperature sensors that descend to a targeted Depth and the instrument is the primary tool for determining physical oceanographic properties. We used the CTD to find a cold-tongueCold-tongue: a neutrally buoyant finger of glacial meltwater that flows out from an ice calving front at depths around 300-400 meters. Here, the cold-tongue is generated by tidal melting underneath the large Cayley Glacier in Hughes Bay. from Cayley Glacier in Brialmont Cove (Hughes Bay) that Gene discovered in the late 1980s. When the CTD detects a cold-tongue, it shows a negative temperature anomaly and a cloudy section of water. Our casts did not find a cold-tongue in this area; however we did see a positive temperature anomaly around 80-120 meters down. This is likely remnant from a CDW upwelling during the past year. The source of CDW in this area may be from the Bransfield Strait (north) or the Gerlache Strait (south). Different oceanographic minds differ on the source, so we sampled the water mass to conduct isotopic studies in hopes that they will elucidate the subject.
Our field installation mission took place at Duthiers Point at the mouth of Andvord Bay. Andvord Bay is a linear fjord that outlets to the Gerlache Strait. On the way, we saw leopard seals lounging on tabular icebergs and flocks of penguins swimming on the surface, jutting out of the water like little black torpedoes. Our assignment was to change the modem in a continuous GPS (cGPS) station so that it can continue to transmit data through an iridium antenna. The job required transporting gear and crew members to the point. Once again, we boarded the zodiacs and zoomed ashore. Gene, Deanna and I scaled a rocky, snow-covered hill with all of our gear and began our work while Mike (LMG electric technician) and Cara (Lockheed Martin field specialist) maintained equipment downhill from us. Although it was a cloudy day, the view from atop the point was spectacular. To the northeast we could make out Rongè Island and the Errera Channel and to the west was Lemaire Channel with the LMG positioned to the north. To the southeast we peered into Andvord Bay and the fjord steep topography culminated upwards at the Bruce Plateau, barely visible under the cloud cover. The install went smoothly and took about four hours, as anticipated. Now, the solar powered cGPS station will continue to transmit elevation data. The data measures crustal reboundCrustal rebound: here, the uplift of the Earth’s crust after a mass of ice has been removed. This rebound on the Antarctic Peninsula is a post-glacial isostatic rebound. as the land rises in response to post-glacial isostasy(glacial) isostasy: a gravitational equilibrium between the Earth’s lithosphere and asthenosphere that responds to a load (of ice) on the crust. This cGPS station has the fastest rate of uplift on the entire continent at 2cm/yr. 2cm/yr may seem minute, but geologically speaking it is quite remarkable. On the way back to the ship, curious crabeater seals and Gentoo penguins escorted our zodiac while snow petrels perched along the snowy coast.
Back on the LMG, our coring work continued. The two kasten cores were sampled and described on the ship. Kasten core barrels are square, as opposed to circular, and equipped with removable metal covers so analysis can begin immediately upon retrieval. We sampled primarily for radiocarbon and grain size analysis. JKC-15 included a brittle star as well, quite an interesting inclusion at the top of our core. At the bottom of JKC-15 was a long turbiditeTurbidite: an underwater avalanche that deposits thick sequences of coarse to fine grained sediment from bottom to top. This arrangement of fine-grained above coarse-grained sediment is called a graded deposit. sequence of little stratigraphic importance for our study of deglaciation. Thus, we sampled extra bottles of turbidite mud and handed them out to the LMG staff as “souvenirs”.
Although we faced the roadblock of sea ice and were delayed, LMG cruise 12-11 was very successful scientifically. We were able to core into sedimentary units not before seen in the Gerlache Strait and discovered modified CDW in Hughes Bay. In fact, we completed all of our cruise objectives except for two field installations that were cancelled due to weather and sea ice. The Gerlache Strait cores will be shipped in a refrigerated container to Florida before they are fully analyzed. Katy and Deanna will likely continue work on these cores for their respective senior theses while I will continue my work on Hughes Bay seawater samples. Overall, the cruise was a fantastic learning experience both scientifically and logistically. Professors Gene, Amelia and Brad did a lot of planning and preparation (not to mention paperwork) for the cruise and it is good for students to see the behind-the-scene work that goes into Antarctic studies. Thank you to all who kept up with our blog; LMG 12-11 science crew signing off.