NBP0505 sailed from Punta Arenas on June 23 with a diverse science party that is collaborating to study the record of sedimentation from three different glacial systems in Chile. On board are eight persons from Rice University, two students from the University of Washington, five scientists from University of Concepción (Chile), and one participant each from SHOA, INACH, and University of Magallane (all Chile).
It took a few days for the Palmer to reach the first study area. During that time everybody prepared equipment, finalized plans, and enjoyed the spectacular scenery of Chile's inner passage. Once in the study area, all aboard worked extremely long hours.
The San Rafael study area consists of several small basins. The outer fjords and middle basin are connected by a narrow and shallow pass that the Palmer could cross only during daylight hours. The middle basin and the inner basin are connected by a six mile long river that can only be navigated by small vessels. After completing a multibeam and 3.5 kHz survey of the outer and middle areas, we began coring, seismic, and small boat operations. A total of 26 cores were attempted and twelve kasten cores and five jumbo piston cores were obtained. Of the nine failed core attempts, eight are attributed to a hard sandy bottom. Seismic data was collected from the Palmer using two fifty cubic inch air guns and then two fifteen cubic inch water guns for a higher resolution survey. Each of these surveys shows laminated sediment packages onlapping onto steep-sided bedrock walls. The final data to be collected at San Rafael was a short sidescan sonar survey. Despite a rocky start, the images from the sidescan system are of high quality and show what are most likely sand waves formed by strong tidal currents.
Small boat operations had to be cancelled on the first day in the area due to extremely high winds but were resumed on the second and fourth days. A landing craft was used to deploy CTDs along the glacier front and a zodiac was used to deploy personnel to retrieve data from a rain gauge set earlier in the year. The Palmer's work boat was used for the first time in science operations and collected seismic data, using a boomer system, in the San Rafael Laguna along the glacier terminus. The boomer data from the shallow water in the laguna is of very high quality and, although of limited extent, promises to be very useful in mapping the most recent deposits. The layered sediments of the laguna lap out onto morainal ridges. Unfortunately, the work boat became stuck in shallow water on the way back out of the river and the boat's rudder was damaged. Although it has been successfully repaired, it was not available for the final day at San Rafael.
All cores collected during this cruise are being split on board and described, photographed, and sampled. This is not standard for cruises on the Palmer but allows for immediate analysis and therefore better selection of additional core sites as well as person-to-person communication among the scientists from different institutions. Surface sediments in the San Rafael area can be divided into two basic types, clean sand or gravelly lags in shallow areas and sandy or silty muds in the basins. Jumbo piston cores record the same basic units. Many of the cores contain abundant bioturbation, fossils, and living flora. Diatoms were observed in smear slide analysis from all cores. Assemblages consist of a mixture of marine, brackish, and freshwater species. Samples have been taken for 210Pb, 14C, foram, additional diatom, protein, isotope, and opal analyses.
We are now in transit to the Penguin and Europa fjords. We anticipate more ice in the work area but less difficulty with narrows and shallows.
During week 2 of NBP0505, we completed our study of the Penguin and Europa fjords. This study area is around 50° S latitude and is the middle location in our transect of three different drainages on the Chilean coast. As we had feared, there was ice cover of much of the inner portion of each of these narrow fjords. Europa was somewhat less ice-choked and thus we concentrated our survey there. Neither fjord had enough open water for small boat operations.
Multibeam swath bathymetry data of the two fjords show several distinct minibasins, similar to what was observed in San Rafael. Unlike San Rafael, these minibasins show a distinct pattern of stepping down from the glacier front, so that each basin is deeper than the one inland from it. Overall, the multibeam bathymetry data does not show any erosional fabric. However, further processing of the amplitude and sidescan data from the multibeam system highlights a fjord-parallel fabric that we attribute to glacial erosion.
We made a total of 20 attempts at coring in this area. 12 kasten cores were collected. One was discarded due to over-penetration and the other 11 were described, sampled, and archived on board. 8 jumbo piston cores were collected and nearly all of them were full. 5 of these were cut on board but three were left uncut. Having this much material to process kept the labs busy! The sediments consisted primarily of either silty/sandy mud or mud. Cores from the ice front sampled mud with very high water content, indicating high sedimentation rates at the ice front. Smear slides were made from samples from each core and diatoms were observed in all slides; assemblages are composed by marine, brackish, and some freshwater species. Coccoliths, silicoflagellates, and foraminifers were also observed in cores from three sites. Decreasing biogenic material was observed with increasing proximity to the ice front.
Seismic data were collected using a 50 cubic inch air gun. This larger seismic source was needed due to the deeper water in Europa and Penguin fjords. The seismic survey shows very thick, laminated sediments in each of the basins; the sediment is somewhat thicker in Penguin fjord. We completed two sidescan sonar surveys. Both surveys were accomplished with no difficulty despite the difficult towing conditions (irregular bottom, sea ice, narrow fjords that don't leave much room for turns). The two surveys show similar results of what appear to be bedrock knobs sticking out an otherwise very smooth bottom. No other distinct geomorphic features were observed.
Lastly, we also conducted a series of CTDs from the Palmer. These were not done as close to the ice edge as we hoped but may help to constrain melt input into the system.
We have concluded this second study area by returning to Punta Arenas for a very short port call. A few people will get off the ship and return home. Two more were just added to this list so that they can return home to board up their Florida houses in preparation for the hurricane that is now in the Gulf of Mexico. While in port, we picked up supplies so that we can take 80 foot jumbo piston cores in our remaining study area. We are now headed south to the Marinelli Glacier on the island of Tierra del Fuego.