July 3, 2006 Options

[Betty_Carvellas]

July 3, 2006

Today I spoke with Dr. Kate Darling, researcher and one of the few biologists in the Earth Sciences Institute at the University of Edinburgh. If you read yesterday's journal, you know that Ian Darling, Kate's husband, is observing birds on this cruise. Kate is actually the one who travels the globe studying foraminifera; Ian is excited to be on board with Kate on his very first science cruise.

Although Kate's doctorate is in animal science (she specialized in large animal physiology), she took twelve years off to raise her family. When she returned to science, her interests shifted to marine biology, specifically to paleoceanography. Her current research is funded by the Natural Environment Research Council, and she holds the title of Advanced Research Fellow.

Kate's work on deck immediately follows our current work with the bongo nets. She also samples plankton, but on a very different scale and for different reasons. She's looking for single-celled zooplankton called foraminifera. Forams, as they are called, form calcareous shells, and their deposits can be several kilometers deep on the ocean floor. These are some of the structures responsible for limestone, chalk, and the White Cliffs of Dover! When studying these organisms in ocean sediments, geologists can look back in time more than 65 million years; that's before the mass extinction event that wiped out the dinosaurs!

Kate collects her samples in two ways. She pumps surface water at approximately 5 meters, for an hour at a time. She also uses a plankton net to sample the entire water column for 100 meters. With an 85 micron mesh (a micron is one one-thousandth of a meter) at the end, her filter lets the very tiny plankton go through while still collecting the forams. Kate is just taking it out of the water and rinsing the net to make certain all the plankton end up in the cod end at the bottom. You can see the net with the cod end in the picture below.


Kate uses a plankton net which goes down and is brought back up vertically in order to collect organisms from a 100 meter water column. Even though she is only studying foraminifera, she collects lots of other plankton which she must sort and discard before doing her own work.

Once she has her samples, Kate will spend anywhere from 8-10 hours each day looking through a stereoscope (a microscope with two eyepieces) which magnifies the organisms 60 times. She first locates the forams by swirling them into the center of her small dish and finding them with the naked eye, and then she tries to identify each one. Kate explained that identification is tricky when there are lots of juveniles like the ones she's been finding in her samples so far. She then picks out each individual organism with the tip of a fine brush and transfers it to a tube containing one of a series of trial buffers designed to extract the DNA without dissolving the organism's shell.


Kate Darling spends 8-10 hours each day looking through her microscope to identify, sort, and save hundreds of forams, tiny zooplankton.

Once she gets her samples home, Kate will analyze one specific gene while other scientists will study the chemistry of the foram shells. All organisms have some conserved genes, genes that are essentially the same. Within conserved genes, there are often variable regions, and Kate is looking for those variable regions specific to forams. And, get this - Kate tells me that there is more variation between the 4000 base pair gene of each foram species than between us and green plants!

Why is Kate doing all this? Paleoceanographers often use forams to look at planetary changes (ocean and climate), because forams have evolved and have different adaptations for living in different climates. When the paleoceanographers see similar forams from the past, they can utilize that information, in conjunction with other indicators, to make assumptions about paleoceanography and past climate. These assumptions are made based on morphology (form), but Kate's work is based on genetics. She has found that, while morphology may indicate that organisms are the same morpho species (based on shell shape), there might actually be several different species among them. For example, one species (based on morphology), G. bulloides, is found from sub polar to sub tropical waters. Kate's work has shown that there are actually seven different genotypes (the DNA found in an organism) among this "one" species, and some have different adaptations. To show what this means, Kate told me of a cruise from the UK to Iceland in the spring. They collected a mixture of G. bulloides for the first half of the cruise, and then found only one type, the cool water forams, the rest of the way. In the summer, they found a mixture all the way, and found the cool water type only north of Iceland. The key here is that the sediments between the UK and Iceland will show a mixture all the way! To sum it up, Kate's work will improve the resolution of the fossil record for the paleo-oceanographers.

Kate told me that she finds her work biologically fascinating, and she loves the interdisciplinary aspect. Her next cruise will be in the Arabian Sea where she'll be starting work to discover when cool water systems started mixing with the southern ocean. It's tough doing Kate's work on board the ship, because sitting for hours at a time trying to balance oneself and focus a microscope at the same time is exhausting. It's obvious that the results are worth the effort!