Photo 1 (right): The entire scientific party on the bow of the R/V Melville.
Photo 2 (below): The TAMU-based scientific party on the bow of the R/V Melville.
The science portion of the cruise is over. It was very successful. We pulled in our last seismic equipment this morning just before crossing into the Peru exclusive economic zone (EEZ). We don't have clearance to collect data in the Peruvian EEZ so all scientific equipment is turned off. We will arrive at Arica, Chile early Sunday morning.
In all we collected literally tons of samples and thousands-of-miles worth of seismic, sub-bottom profiling, and multibeam sonar data. We surveyed portions of the ocean floor that have never been studied to the degree we have done here. We have collected over 100 meters of sediment from the Cocos and Carnegie Ridges, and the Peru Basin. We have filtered for alkenone analysis approximately 60,000 liters of surface seawater along the path we have traveled. For surface water trace metal and oxygen isotope analysis we have sampled about 60 sites. Finally, for uranium, thorium, and neodymium isotope analysis we have collected 70 water profile samples (20 liters each) from 9 sites along a latitudinal gradient from about 8degN to 8degS. Now, the REALLY hard work of analysis and interpretation of the data and samples collected begins!
Figure 1. Our cruise track line. The blue line shows the path for which high-resolution seismic data was collected along our path. The yellow line shows the path for which low-resolution seismic data was collected. No seismic data was collected on the red portions of the path. However, on the entire path (blue, yellow, and red) multibeam sonar and sub-bottom profiling data were collected. Also, along the path several tons of sediment, surface water, and water depth profile samples were collected.
Once the cores are sliced open lengthwise, one half is put into storage as an archive, while the other half is sampled and described aboard the ship. Representative microscope slides of the sediment smears are made and described for each cut section of core. Daniel Rincon, a scientist from EAFIT University in Colombia, is shown in the photo at right at the microscope station in the main lab of the ship.
Photo right: Night water sampling: Front, L to R: Ruifang Xie, Ajay Singh, Jessica Schubert. Back L to R: Ashley Hague, Matthew Schmidt, and Jennifer Hertzberg. Sampling the CTD rosette (water sampler) in the even earlier morning hours. Samples from this cast represent the deepest of the cruise so far: 4200 m (or 2.6 miles)!
Photo below: Night watch: L to R: Chris Paul, Brandi Murphy, Pratigya Polissar, Dan'l Lewis, and Heather Ford. Working hard at the watch station in the main lab during the early morning hours.
Photo right: Graduate student Jennifer Hertzberg attempts to get an uncontaminated water sample for trace metal analysis of surface seawater.
With Matthew Schmidt she is trying to quantify the relationship between barium concentration and sea surface salinity. If successful, they'll be able to use this relationship to reconstruct past salinity changes in the region, and relate these changes to past climate variability.
We've finished surveys of the Cocos and Carnegie Ridge areas, and are steaming toward our final survey area in the Peru Basin. Along the way we've retrieved several sediment core and water samples. To give you an idea of the route we've taken so far, follow the colored line in the figure. The line is the path we've taken, and the colors along the line give snapshots of the changing temperatures of the surface seawater. We started off the coast of Costa Rica with surface sea water temperatures (SSTs) of about 28 degrees C, and are currently in an area with SSTs of about 18 degrees C, a change of 10 degrees C! The reason? We've crossed a zone in which deeper colder waters are being upwelled along the equator and south of the equator.
Figure above right. Sea-surface temperatures (SSTs) along the path we've taken so far. Note the two areas where the path is convoluted--these are the areas on the Cocos and Carnegie Ridges where we've performed extensive seismic surveys and have collected several sediment cores.
We decorated cups and sent them to the bottom of the ocean (2900 m or about 1.8 miles) with the multicore apparatus. The pressure from the overlying water is the same in all directions so that the cups barely change their shape and only their size. The compression factor was about a factor of 2.5.
It's been a busy night of coring. We collected the longest core of the cruise so far--about 17 m!
Photo above: cups before their descent. Photo to the right: compressed cup after return to the ship.
We've sampled one site within the Carnegie Ridge area, and retrieved multicores, and piston cores. Much of the coring was performed in the early morning hours in complete darkness (see photo of multicore coming back up in the dark). The areas we've "swathed" so far with multibeam bathymetry, sub-bottom profiling, and high-resolution seismic reflection are shown in the figure. Tonight at about midnight we stop the seismic data collection and core three new sites. This will take about 24 hours, and then we leave the Carnegie Ridge area for the Peru basin, collecting water depth profiles along the way (see map).
Photo of Pratigya right: Pratigya Polissar (Research Professor from Lamont-Doherty Earth Observatory) is filtering alkenone-producing haptophyte algae from seawater.
Photo of Shiloh and Heather below: Shiloh Schlung and Heather Ford (graduate students from UCSC) are sampling seawater for nitrate, phosphate, water isotopes, DIC, and alkalinity to compare with the hydrogen isotope ratio of alkenones.