ANT-XXVI/2, Weekly Report No. 2

5 December - 11 December 2009

We’ve been at sea for two weeks now, and daily life has become routine. Breakfast, lunch and dinner alternate with Hydrosweep and Parasound watches and work on deck and in the laboratory. Time is flying by. Today, December 11th, at 6:10pm we crossed 60°S at longitude 115°07.7´W. That is to say, we’re now in the area covered by the Antarctic Treaty. Air and water temperatures are around 3.7°C, and it doesn’t get dark at night anymore- it’s summer in the Southern Hemisphere.

The initial plan was not to arrive here until next week, but we’re on the run. Luckily, we have two weather experts on board from the German Weather Service in Hamburg, who can forecast the weather and sea conditions and warn us ahead of time. Three days ago it became clear that a strong low-pressure system with high waves and storms was approaching. If we had stayed on the track we had originally planned, we’d now be surrounded by an angry sea. The ship would have been tossed around as waves washed over the deck. Nothing would be secure on board and we wouldn’t have been able to work or sleep. Weather data showed wave heights of 9.5m in our initial target area, a tempest!  We decided to throw in the towel and head south. Over the course of two days, we travelled 550 nautical miles (ca. 1000 km) with four machines to a study area south of 60°S, which we will reach around midnight. Here, the ship is bobbing gently on waves of only 2-3m. We’ll have to work all day and night, but it' sure was worth it!

A week ago, Santa Claus came onboard. Quietly, he made his rounds on the ship and distributed sweets. I saw him clearly from behind on the C deck. As he made his way down the hallway, he suddenly stopped and looked down. Indeed, there were shoes that had been cleaned and left outside one of the doors, with the hope that Santa would find his way to the middle of the Pacific!

After our work in the Eltanin impact area, we steamed in northwesterly direction towards the East Pacific Ridge. We crossed a >5000m-deep trough structure and deployed the CTD with rosette, the MUC (multi corer) and the piston corer. The CTD probe (‘Conductivity, Temperature, Depth’) is lowered to the seafloor on a cable, which sends electric signals back to the ship, measures conductivity (salinity) and temperature in the water column. This provides us with information about the water-mass structure at the study site. An additional sensor measures primary productivity in the water. The probe is surrounded by 24 plastic cylinders (11liters each) that can be remotely closed to collect water samples from different depths in the water column. Different chemical and biological measurements will be conducted on these samples (e.g., analyses of dissolved nutrients, stable oxygen and carbon isotope ratios, chlorophyll concentrations, pigment distributions, distribution of micro organisms, gases). Since the water samples from each water depth are limited, the sampling from the bottles happens according to a carefully crafted plan. The CTD measured a water temperature of around 0°C at the bottom of the trough. This is an indication for the presence of cold bottom water, which is formed under a thick ice shelf in the Ross Sea more than 4000km to the southwest. The cold bottom water spreads northward into all major ocean basins and constitutes an important component of the global ocean circulation system. Our scientist from the University of Hawaii was particularly happy about this, because the water and sediment samples collected from this location will allow her to develop methods to reconstruct changes in bottom water formation and distribution during short-lived climatic changes in the past.

On December 6th our track crossed a crescent-shaped chain of seamounts. Available bathymetric maps suggested water depths of only 40m above the seamounts and this was reason enough for a short detour to map the area. As we approached the first seamount the water depth indeed decreased rapidly; however, its ~4km wide plateau was 500m rather than 40m deep. This is nothing unusual for the Pacific, where seamounts such as these with a plateau at the summit (called guyots) are common. The seamounts have now been mapped for the first time and later we’ll have the opportunity to name them. We obtained a surface sediment sample from the summit of this seamount, which contains exclusively foraminifera. These are unicellular organisms the size of sand grains that produce a carbonate test of several small chambers. The species distribution, chemical composition and isotope ratios of elements in the carbonate tests are important in reconstructing past environmental conditions.

On the way to the East Pacific Ridge we were at first disappointed not to find sediments at 4000-5000m water depth worth coring, but on December 8th we finally found a ‘seamount’ covered with sediments and took a 17.26m-long core from 3000m water depth. Further along our track the Parasound showed thick sediment layers, and we were able to take additional cores from sediments deposited on ~40 million year old oceanic crust. This allowed us to conduct so-called ‘pre-site survey’ work for a deep-sea drilling project. A pre-site survey is a combination of bathymetric, seismic and marine-geological investigations that are required at locations proposed for deep-sea drilling. It was just after this that we received the storm warning from the meteorologist on board and began our detour to the south.

Day in and day out, two shifts composed of a broad international community work in alternating 12-hour intervals to open (‘split’) the sediment cores, describe the sediments, take initial samples and assign ages to the cores using the species composition of microfossils. Rudi the reindeer (from Switzerland) and Addy the penguin (home unknown) are also helping out. For example, they intensively studied a manganese nodule that was found in one of the sediment cores and discovered certain similarities between the nodule and themselves. (Although the manganese nodule is much older!) We are excited to see what else Rudi and Addy will find in the coming days. Addy has another important role on ANT-XXVI/2. He is a worldwide ambassador and is accompanied by a school teacher, who is assisting us on board. More about this in the next report.

All participants are still enjoying themselves and are in great shape!

Rainer Gersonde
(Chief Scientist ANT-XXVI/2)