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The MOCNESS (monster)
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Week 2
10 July 2006

Searching for the Elusive Element by Using Physical Oceanography

Introduction: For each of the remaining weeks, I’ll feature a different research project being conducted on board.  The general goal of all the groups is the same: To understand the process of transformation from the blue water zone (little or no phytoplankton) to the green water zone (areas of high concentration of phytoplankton) and the role played by iron in this transformation.

Each group is examining a different facet of this process, whether physical, chemical or biological.

 

 Reading Comprehension Tip: Some of you may wonder whether you’ll be able to understand the science. Breaking information down into sections can help you identify the basic concepts.
Another tip is to survey illustrations and charts before you start. Go back to the illustration: Chlorophyll Concentrations, The Antarctic Circumpolar Current.

 

Physical Oceanography – The Zhou Group

  1. What is the objective of the project? What do you already know about the topic? What is it you want to learn this time?
  • The objective is to understand the physical processes involved in the transformation (change) from the blue water zone to the green water zone. Understanding the physical processes is fundamental because they are the driving force for the other processes. In 2004, Meng Zhou studied the ocean circulation patterns of the area. Now in 2006, he is studying the seasonal variations in currents. His group is also studying the vertical and horizontal mixing that takes place between the Antarctic Circumpolar Current (ACC) and the shelf waters. The water of the ACC is iron poor and the shelf water is iron rich.

 

  1. Why do you want to do this?

  • The sea is warming and scientists want to know how the warming will affect the Antarctic ecosystem. Scientists want to be able to predict the impact of change. To understand this system, scientists need to now how the physical processes drive the biochemical processes. With this warming, some species will adapt and others will disappear.

 

  1. Where are you carrying out the project? How is the location important to finding out what you want to know? (Look again at Chlorophyll Concentrations map)

  • The location of the project at the Shackleton Fracture Zone in the Southern Ocean is critical to understanding the transition between the blue and green water zone. Here the current is squeezed through a gap between the Shackleton Fracture and Elephant Island. Here scientists can look at the process that produces eddies. They want to know how strong the current is and what pathways it takes. How does the strength of the jet affect the eddies? What is the seasonal variability of the Antarctica Circumpolar Current?
Chart 1 - CTD Stations
Chart 2 - Drifters
The ACC is driven by strong westerly winds, the strongest winds in the world. The winds transport heat northwards and the eddies transport it southward.
  • The open patch of ocean allows an eastward current, the Antarctic Circumpolar Current or ACC, to flow around the globe. It is the worlds largest current, carrying 130 times the volume of water of all the world’s rivers combined
  • Eddies are swirls of water currents that are spun off from a main current or that are forced by the wind.
  • The ACC is not a steady current, but is made of constantly evolving waves and eddies. When averaged over time, these eddies produce the flow we call the ACC.

from The Antarctic Circumpolar Current
(ACC) presentation by Richard Karsten Acadia University

 

  1. How are you gathering, processing, and analyzing information?

  • We use surface drifters to measure the surface current. Drifters have a body about 25 cm. long. At the top of the drifter, a transmitter sends location information to a satellite 8 times a day. This information is sent to the ship once a day. Twelve drifters will be used during this cruise. They have a lifespan of 1-2 year. Other instruments include the ADCP (Acoustic Doppler Current Profiler) which measures ocean currents using sound. CTDs (conductivity, temperature, depth) are used to look at temperature and salinity in order to determine water mass and density distribution. Finally, the scientists use the MOCNESS (Multiple Opening and Closing Nets Environmental Sensing System) to catch zooplankton at different depths. See Chart 1 (from a previous cruise) for CTDs locations; Chart 3 for paths of drifters and Photo of the MOCNESS.

Chart 1 - CTD Stations
Chart 2 - Drifters
Chart 1 - CTD Stations Chart 2 - Drifters

 

  1. When? – Why are you choosing this time of year?

  •  We want to sample at this time of year because deep mixing occurs in the winter.

 

  1. What factors affect the success of your project?

  • All the instruments need to be working, the sea has to be calm enough to deployment the instruments, and a cold front is necessary to produce a cooling event.

 

  1. Who does what? What is the role of each person in your group?

  • Yiwu Zhou is a research associate who works with the CTD and does data processing. Ryan Dorland, a PhD candidate, works with the ADCP and also does data processing. Di Wu, a PhD candidate handles the drift data and analyzes temperature and salinity information. Marina Frants, a PhD candidate specializes in satellite altimetry. Meng Zhou, the principal investigator (PI) for this group looks at all the data in real time. He determines the locations where samples will be taken based on the information his group processes. (More biographical information in the section on “The Team.”)
Yiwu Zhu, Research Associate University of Massachusetts, Boston
 Ryan Dorland, Graduate Student Di Wu, Ph.D. candidate Meng Zhou, Associate Professor
Yiwu Zhou,
Research Associate
Link Biography
Ryan Dorland,
Graduate Student

Link Biography 		Di Wu,
Ph.D. candidate

Link Biography 		Meng Zhou,
Associate Professor
Link Biography
The physical oceanography team processing data
The physical oceanography team processing data

 

  1. Next Steps

  • One step is to come back in order to understand the evolution of eddies – how they are enriched and depleted. Another would be to examine how the plankton community evolves.

 

Extension Activity: What physical process(es) affect(s) populations and/or distributions of plant and/or animal life where you live?



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NSF Office of Polar Programs, Antarctic Sciences Section
This special report was made possible by the NSF Office of Polar Programs, Antarctic Sciences Section, Award Nos. ANT04-44134 University of California-San Diego Scripps Institution of Oceanography (B. Gregory Mitchell, Farooq Azam, Katherine Barbeau, Sarah T. Gille, Osmund Holm-Hansen); ANT04-43403 University of Hawaii (Christopher I. Measures, Karen E. Selph); ANT04-44040 University of Massachusetts Boston (Meng Zhou); ANT04-43869 Woods Hole Oceanographic Institution (Matthew A. Charette),  for the study entitled "Collaborative Research: Plankton Community Structure and Iron Distribution in the Southern Drake Passage".