Southern Ocean Iron Experiment (SOFeX) Cruise
January 5 - February 26, 2002


Skip to Log Entry from the USCGC Polar Star
February 19, 2002: Day 46

R/V Melville:
Position: 53 degrees, 25 minutes South, 168 degrees, 5 minutes West

Photo: Bob Bidigare changes out a filter from his last "In Station" at the Southern Patch. With this much material, he should get a good signal for all his biomarkers.

R/V Melville Log Entry: We are chasing down the Northern Patch and whereas Ken Johnson made it look like waking up on Christmas morning and going downstairs to open presents, this is more like waking up New Years Day with a bad hangover, stumbling around looking for some Alka Seltzer. The patch is strung out in tiny thin filaments up against a cold front with no indication (yet) of the second infusion. We are sniffing and feeling our way along a temperature front with tiny narrow fluorescence signals and wimpy SF6 values. High fluorescence accompanies some weak SF6 and builds until it disappears under the colder water to the north. No big signals yet, but we are on the scent!

About Pigments

It was just a few years ago that I first saw the east coast colors in the fall. Spectacular. There was every shade from dark green, yellow, bright orange, red, maroon and every color in between. "Carotenoids!" I cried out in excitement (glad that there was no one else in the car) and amazed at the variability in the color of these accessory pigments. Yes, when we think of plants, we think of chlorophyll, this is what makes them green. But a plants ability to harvest light energy is dependent upon their ability to capture light of many wavelengths and transmit this energy to the chlorophyll molecule. On land we only see this during the time when chlorophyll is resorbed and broken down in the fall. This is when we can see the accessory pigments. They give the plant or phytoplankon more latitude and are crafted for certain light levels and situations.

Wouldnt you know it, phytoplankton have these also. The interesting thing is that each has a different set of pigments, the analysis of which can be used as a finger print to identify the presence of certain kinds of phytoplankton, or taxa. For instance, diatoms have fucoxanthin and dinoflagellates have peridinin.

What is nice about phytoplankton is that you dont have to wait until fall. You just suck-em up onto a filter, grind em in a solvent, and injected em onto an instrument called a High Performance Liquid Chromatograph (HPLC) where up to twenty different pigments are separated out and their concentrations quantified. Bob is interested in using pigments as chemotaxonomic indicators of the phytoplankton present. Through the analysis of these pigments over time, Bob can characterize the shift in species composition in the enriched patch. This tells us a lot about succession of the particularly dominant species.

In addition, some of these pigments can be preserved in the sediments and as such become unique paleo-proxies for phytoplankton grown and the flux of phytoplankton detritus to the deep sea. What is a paleo-proxy? It is specific evidence for something that occurred in the past. These paleo-proxies are also known as "bio-markers" indicating that they are specific to a certain organism. Through the distribution of these paleo-proxies in the sediments, one can recreate the phytoplankton assemblages of the past.

It gets better: plankton take up carbon isotopes from seawater in ratios that reflect their growth rate, temperature and nutrient availability. Bob and his colleagues believe that the isotopic composition of these biomarkers in sediment cores can be used to reconstruct past climate (temperature, atmospheric carbon dioxide and nutrient concentrations under which the phytoplankton grew). Now we are talking really big science!! But does it really work? What is missing is the testing of these proxies, essentially testing whether they really do function in these ways. This is what this experiment can do. We can try to mimic an ice age flux of iron, change the growth rate of the plankton and see how these biomarker compounds change in proportion to one another, then measure their isotopic composition and Viola! You are calibrated. Take a core and you reconstruct the glacial ocean. But first, lets find the Patch.
Kenneth Coale, Chief Scientist.

USCGC Polar Star:

USCGC Polar Star Log Entry: We continue to be amazed at how stable the southern patch is in terms of its location and with respect to the general characteristics of this iron-induced bloom. Certainly our ship drifts much more as we stop to take samples (driven mostly by the winds) than the water and patch underneath. Our initial fear was that without positioning buoys tracking the patch, wed never be able to relocate.Well, in the past 6 days weve done a lot of in and out mapping, and each time we return we find our now familiar patch indicators (SF6, Fv/Fm, etc.) in very much the same location.

Today we had a brief, but enjoyable morning of bright blue sky- our first in the past week. I hope the ocean viewing satellite sensors overhead had a chance to snap an image or two of this patch and surrounding waters. You can quickly forget how nice it is when there is little movement on the ship in calm waters. Everything, from our sampling with the CTD/Rosette, to working in the lab, to eating and sleeping become much easier. Its as if for every factor of two increase in wind speed or wave height, there is a factor of 20 increase in difficulty in working at sea. Something like the Richter scale is needed to classify comfort conditions here, and today would have been a very low number for these calm conditions.

Todays calm weather brought out sunglasses and smiles, especially on the decks. Shown below are two of the main USCG marine science officers and technicians assigned to our group, Paul Rodriguez (the one with the shades) and Scott Chen. Along with the other MSTs (marine science techs), this USCG group and their commanding officers have been supportive of our efforts from the start. Dont get me wrong, this ship is unlike any science or UNOLS ship I have been on, but within the limits of the ship and the regular USCG duties, weve managed to meet our objectives. In part, weve been fortunate that the weather has cooperated to allow more work than might otherwise have been possible on this ship, which has a bottom that was described to me by the Captain as being "egg-shaped". But in addition, the support of the MSTs and crew in general, especially on all of those not so sunny, not so calm and all too hectic workdays, has made all of this possible.

Tonight we make our last "butterfly" pattern map of the patch, in anticipation of some final vertical profiles during the first half of the day tomorrow. As usual, our underway-sampling crew is up for the task. In our photo of the day below, Joe Tegeder (left) and Kevin Mahoney show off the latest lab fashion wear- purple lab gloves. This duo volunteered to join our cruise after having just completed another science cruise on the Polar Star. For us, this meant two strong hands at sea (or is it four hands?), and an edge coming on board with inside knowledge of this ship. They are both graduate students at the University of Southern Mississippi and have a keen interest in the biogeochemistry of the Southern Ocean. From what I have seen, they have a bright future ahead of them.

Ive been interrupted quite a few times tonight as the excitement builds. Everyone is wondering what we will find in tomorrows final sampling in the patch. And how do we compare a bloom in the iron patch from some of the high and low chlorophyll areas we see outside the patch? And just how long would you need to be here to see the end of this bloom? We have a good idea of the seasonal dynamics of this region thanks most recently to a major US Program, JGOFS (Joint Global Ocean Flux Studies) that visited this area in late 1997 through early 1998. Part of the puzzle from my perspective is to compare these iron induced conditions of enhanced production, to the natural blooms that occur here. We have one last chance to view this man-made bloom tomorrow and then its a long haul back to shore.

Its an exciting night ahead as our attention is now focused on the end of the experiment. Til then,
- Ken Buesseler

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