Welcome to the Murray Field Team Web Site for Iceberg III - "Free-drifting icebergs as proliferating dispersion sites of iron enrichment, organic carbon production, and export in the Southern Ocean."
We will post weekly updates specific to the Murray Field Team research. Be sure to visit the Iceberg III's official website, hosted by the Monterey Bay Aquarium Research Institute (MBARI) to see information on individual aspects of the overall project, including daily posts, profiles of all 31 members of the research team, detailed equipment descriptions, and an extensive photo gallery.
The Murray Field Team is up to its old antics, venturing deep into the southern hemisphere to feed its fascination with life at the molecular level. This time, the objects of interest are free-drifting icebergs that originated from various regions of the Antarctic ice shelves and have concentrated in a region of the northern and northwestern Weddell Sea known as "Iceberg Alley." These free-drifting icebergs are hot spots of biological activity and therefore likely become regions enriched by organic matter. In addition, although the Southern Ocean is typically nutrient rich (in forms of nitrogen, phosphorus and silica – all important to primary production), it is the largest iron-poor region in the world. One of the primary objectives of this research cruise is to determine whether the icebergs are sources of micronutrients such as iron. We will measure rates of primary production and other biological processes within the iceberg’s zone of influence to see if there is a positive effect of the iceberg in comparison to non-iceberg impacted waters. The presence of free-drifting icebergs, and ablation from these icebergs, may contribute iron directly through melting processes, or indirectly through localized upwelling, resulting from destabilization of the water column by the iceberg.
Why do we care about the pelagic ecosystems associated with free-drifting icebergs? Large icebergs – including some longer than 18.5 kilometers (~11 miles) – have been calving from the Antarctic ice shelves more frequently in the last decade. Smaller icebergs may yield smaller IZIs, but their increasing frequency could enhance their collective effects. As ice continues to migrate from the ice shelves to the open sea, this project hypothesizes that increased primary production, and carbon sequestration, from nutrients associated with free-drifting icebergs could affect the global carbon cycle. Discussions of global climate change have extended beyond the confines of academia and into the public eye, where the role of science is critical in better defining how carbon moves through the environment.
Dr. Alison Murray and the Murray Field Team are part of a multi-disciplinary research group that aims to develop an integrated profile of the role that free-drifting icebergs and the associated nutrient enrichment plays in the carbon cycle by answering the following questions:
- What is the relationship between the physical dynamics of free-drifting icebergs and the iron and nutrient distributions of the surrounding water column?
- What is the relationship between iron and nutrient distributions associated with free-drifting icebergs and the organic carbon dynamics of ice-attached and surrounding pelagic communities, such as microbes, zooplankton, and micronekton?
- What is the relationship between organic carbon dynamics of the ice-attached and surrounding pelagic communities and the export flux of particulate organic carbon from the mixed layer?
- What is the estimated combined impact of the population of free-drifting icebergs in the Weddell Sea on natural enrichment, carbon production, and particulate carbon export from the mixed layer?
In 2005, Dr. Ken Smith, our project's Chief Scientist, and fellow researchers completed a preliminary cruise, Iceberg I, to explore the viability of this project. The first iceberg expedition for the current project occurred in June 2008 on the Iceberg II cruise. The priorities on Iceberg II were focused on engineering/instrument testing, in which we studied two icebergs SS-1 and A43K. For Iceberg III, the Murray Field Team will explore the role of organic carbon dynamics mediated by the microbial community. We will work directly with the Phytoplankton Team, led by Dr. Maria Vernet; the MOCNESS team, led by Dr. Ron Kaufman; and the Iron Men, led by Dr. Ben Twining. We will discuss each of these teams and how our research interfaces in the next few weeks.
The Murray Field Team will be collecting water samples to quantify several aspects of the microbial communities in the IZI and far afield from the iceberg, and we will discuss each of the tests, or assays, in detail in forthcoming posts.
- Bacterial Abundance:We will attempt to enumerate cells while at sea using a high resolution microscope (though this can be challenging in the best of weather conditions!) and archive samples for automated counting using a flow cytometer, and for probe-targeted species/group-specific enumeration.
- Microbial Growth Rate: We will determine the rate that bacterioplankton cells make proteins (as a proxy for growth) by measuring incorporation of leucine, an amino acid, labeled with tritium (a hydrogen isotope).
- Community Livelihood: We will prepare four enzyme assays, including chitinase (which targets N-acetylglucosamine, the subunit of chitin), phosphatase (which cleaves organic phosphorus from biomolecules), ß-D-glycosidase (which targets glucose-sugar), and aminopeptidase (which targets peptide bonds).
- Microbial community fingerprint: Community composition profiles (to be run at DRI post-cruise) will determine 'who' is there based on detecting sequence variants in the SSU rRNA gene, encoded in genomic DNA, and simultaneously, we will create complimentary DNA (cDNA) from ribosomal RNA to determine the identity of the active component of the community.
- Culture Experiments: We will be working cooperatively with the Iron Men and the Phytoplankton Team to monitor the microbial community’s response to seawater culture experiments with chemical additions, including amino acids (AAs), iron (Fe), carbon (C), and Zinc (Zn) or Cobalt (Co) over time (16 days) and no additions to determine the levels of iron-limitation in both phytoplankton and bacterioplankton in IZI and far afield waters.
Barring breaching whales, 25-foot seas, or other unforeseen circumstances, we're scheduled to return to Punta Arenas on 15 April 2009, so stay with us for the next 5 weeks as we explore the fascinating trajectory of these wandering ice-borne communities and their role in the global carbon cycle.