Southern Ocean Iron Experiment (SOFeX) Cruise
January 5 - February 26, 2002
Skip to Log Entry from the USCGC Polar Star
February 17, 2002: Day 44
Position: 54 degrees, 30 minutes South, 170 degrees, 6 minutes West
R/V Melville Log Entry: As we head north, we are working up our data from the latest South Patch studies. We are sharing with you the data that we are sending to the Polar Star so that they may be able to more effectively plan their studies (and you can plan your day). All values are tentative and as yet, uncalibrated but the relative magnitude of the properties should be correct and they indicate some very significant findings.
First the larger picture. Over the last few days, we mapped the surface distribution of parameters, sniffing as we went using sulfurhexafluoride (SF6) as our guide. (SF6 contoured over the Southern Patch. Note black dots indicate position that SF6 sample was taken.) SF6 was measured by Dr. David Cooper, formerly of, University of Miami, Woods Hole Oceanographic Institution, Plymouth Marine Laboratory, University of Wisconsin and now a mercenary geochemist and atmospheric scientist living on a home/farm in Arkansas with wife Kim and kids. During his tenure at Miami, David built a unique instrument for the measurement of SF6 unlike no other in the world. It uses no cold traps and was readily adapted at sea for automatic operation. His figures of SF6 confirmed the location of the iron-enriched area. We were so lucky to be able to coax him away from his life on the farm.
Depicted in the next figure are a series of four images (Black lines are the ship tracks). The top left indicates the photosynthetic energy conversion efficiency of phytoplankton, red is for happy cells, blue is for sad cells mapped over the experimental area. Remember Max and Michals (Rutgers University) FRRF work with the flashing lights? This is it! You can see that in the area enriched by iron, the cells are very happy and in the second plot, you can see that they really became much more productive, making lots more chlorophyll than their iron deficient brothers and sisters. In the top right panel is depicted the concentration of chlorophyll. Whereas these values represent something of a composite image, the actual values were both higher and more variable than those reported here. What happened to the water they grew from?
The third plot shows the concentration of carbon dioxide gas in seawater. Bill Hiscock, Dr. Xiaorong Zhu and the Miami group are measuring this parameter continuously. When the phytoplankton grew, they took up carbon dioxide from the surrounding waters, in this case quite a bit. Lower values of carbon dioxide look blue, and higher values appear red or yellow. In a manner similar to carbon dioxide, nitrate and silicate was also depleted. Dr. Mark Brzezinski (UCSB) has been measuring both dissolved silicic acid and taking samples for biogenic silica analysis. His preliminary results indicate that diatoms are taking up silicic acid at a rate proportional to the other macronutrients (more on this later). Whether this results in the export of carbon, we dont know yet.
In the fourth panel one can see an image taken by the SeaWifs Satellite, whose ocean color-imaging camera is used to quantify chlorophyll in seawater. You can see that the signal from our experiment can be seen from outer space and is spatially coherent with the signal we observed in our transects (dark lines indicating ships track) and it is located in the same place. This is a big wow!! When we zoom way back, we see that there are regions of the Southern Ocean that also have higher concentrations of chlorophyll, but these regions do not have the healthy cells as observed inside our Patch. How do we know? Fv/Fm signal is low. So, the oceans are patchy all over the place. This may be another valuable aspect of these kinds of experiments that is to enable oceanographers to study variability in production and the processes that contribute to it.
So what did things look like closer up? Gotta ask the phytoplankton. Sara Tanner (MLML) has been doing phytoplankton tows every day off the fantail. Sara is an expert in phytoplankton taxonomy and biological oceanographic analyses and one of John Martins first TAs at Moss Landing Marine Laboratories. When we compare Inside Patch tows with Outside Patch tows, there is a big difference just by our eyes. When Karen Selph (University of Hawaii, working with Mike Landry) takes a closer look we see not only a greater abundance of cells in the enriched patch, but there are more chloroplasts and chlorophyll inside the cells. In addition, the cells are generally larger and there are more taxa represented in this large size fraction, as if iron enrichment also increases diversity. All these results await confirmation but we feel fairly confident in these preliminary conclusions and excited about what the scientists on the Polar Star and North Patch might tell us.
USCGC Polar Star Log Entry: We are roughly at the mid-point of our occupation of the southernmost SOFeX study site. In a very short time, we have become more efficient at sampling and based upon initial data, more selective about what measurements we think we need to optimize our limited occupation of the study area. Our survey studies continue to go very well, and in my last report, I claimed that a map of photosynthetic efficiency (Fv/Fm) was clearly linked to the addition of iron some four weeks ago. Well, shown here is the reason we (and the prior SOFeX teams) can so clearly make this assumption.This is a map of SF6, with a "hot" spot centered around 66 degrees south, 172 degrees 15 minutes west. If you compare this map to yesterdays Fv/Fm plot, you will see an excellent correlation between the passive tracer SF6, which tells us we are in the right area, and Fv/Fm, which is elevated in response to enhanced iron. Thanks Laura and Leah (and Ed) for this picture.
Well, this experiment is not just about SF6 or Fv/Fm, but loads of other parameters. Since we have such a relatively small team, much of the careful lab work that is required of us, is related to collecting and processing samples for later analyses on shore. Shown here is three of our group, caught in the act of sample processing after one of our sampling stations. Melissa Coggeshell (far left) was living in McMurdo when she joined our group as a replacement for a Chinese scientist who unfortunately could not join us. In the center, Chrissy van Hilst, is on loan from the Bermuda Biological Station for Research where she works on a major time-series program and has gained considerable experience in a wide range of biological and chemical procedures. Shes been a great asset in the lab when we try to figure out some of the sampling protocols being asked of us by scientists who have sent us requests for samples, but they havent seem to have sent us all the right gear or reagents for processing. On the right is a recent Woods Hole Oceanographic Institution Research Assistant, Craig Herbold. Most of his work at WHOI has been closer to shore, but here hes enjoying the ride in the open ocean (not really) and up at all hours giving a hand with lab work and conducting his own research into surface water transport using radium isotopes.
Ill introduce a few more faces in the coming days, and have a call out for more shots showing our gang of USCG marine science techs- these guys and gals take care of all of our science needs, and without them, wed be sunk (and I know thats a word I shouldnt use on a ship). I will however, take this moment to introduce one more vital member close at hand to my job, namely Steve Pike. He works with me at WHOI, and comes with both science smarts (a MS in marine chemistry) and seagoing savvy, as an ex-fisherman and skipper of a fishing boat off New England. Talk about an ideal combination to have in this situation!
This photo shows Steve (the good looking one with the blue hard hat) and my backside, as we hang one of our battery-powered pumps over the side of the ship. We have better pictures of the pump, which is used to filter hundreds of liters of sea water at a known depth through filters of various size pores, to separate the marine particles that we think are sinking in the ocean (the large ones) from those that settle only very slowly. Whats great about Steve is his 'can do' attitude and constant offers to help not only with my science program, but the larger project in general. In fact, if it were not for Steve, none of the equipment, chemicals, gas cylinders, reagents, and sampling gear would have made it on the Polar Star in Seattle or on route via other ports, including our final departure point in McMurdo. Talk about a logistical nightmare. He deserves considerable credit for getting us the resources to do the job and working with USCG to get us set up in this far flung part of the world.
Tonights all night job, is to follow a transect, or line of sampling stations that originate outside the study patch, and cross through a range high and low chlorophyll settings identified in a recent satellite image of the area. I hope there is more to tell about this story in a coming report. In fact, outside of this small SOFeX study region, the waters of the Southern Ocean are unique and interesting in many ways to oceanographers and we feel we are lucky to be studying this remote part of our ocean planet.
Thats all until we reach the other side of the patch.
- Ken Buesseler