Picking with Needle or Brush?

The Japanese Hirofumi Asahi from the Korea Polar Research Institute uses microfossils to tell about the changes in the Bering Sea and Arctic Ocean since millions of years

By Kirstin Werner

A micropaleontologic sample on a microscope tray. (photo: Hirofumi Asahi)

Slowly the left hand pushes the tray from left to right. The eyes follow the tiny needle tip under the stereomicroscope. The right hand smoothly guides the needle in sinus curves over the black tray: up and down, up and down, up and down. Without stopping the needle drives the eyes along angular or softly rounded, yellow, black or transparent rock crumbs, along glassy pins and spiky brown particles. It also passes whitish grains sometimes lustreless, but sometimes as shiny as porcelain can be. They may look like small snails, or appear as tiny postal packages. On one of these white lustreless packages the needle stops. “I could never pick with a needle”,  my colleague Hiro smiles, making me look up from microscope work. “I would not know how to hold it. My hands are too shivery for using a needle.” Among micropaleontologists there a those picking with a needle and those using a brush. Picking with the brush is safer as fragile calcite grains are not going to break. The needle has a steel handle that fits better in the hand but bears the risk of destroying the sometimes very thin-walled parcels already with the first tip.

Hirofumi Asahi from the Korea Polar Research Institute in Incheon 

studies the history of the Arctic Ocean and the Bering Sea.

Hirofumi Asahi uses a brush. For many years, the Japanese has been working with the petite white chalky grains, called planktic foraminifera. “I am fascinated by viewing the ocean floor under the microscope”, he says. Planktic foraminifera are dust-sized, single-celled organisms that float as zooplankton through the upper few hundred meters of the oceans. After their life cycle ended, they sink to the ocean floor. Their calcareous shells, the white lustreless packages, remain buried in the seabed. Even after millions of years they can be found in deep layers of the ocean floor. Micropaleontologists use these fossilized shells to learn about the history of the oceans. “I actually chose foraminifera on purpose as I liked the idea to work with microfossils that can also be applied to geochemistry. I am not that much confident on my taxonomy skills. So I wanted to have more evidence by additionally looking at their stable isotopes or magnesium to calcium ratios which tell about the water conditions the they have lived in”, Hiro Asahi explains. During his master program at the Japanese Kyushu University he taught himself how to distinguish between different types of foraminifera. “My supervisor didn’t have much of an idea about foraminifers so I had to go talk to some taxonomists. And I read lots of books and guides about the different species. Tough way.” Foraminifera build their calcareous shell from the chemical components of the surrounding water. Paleoceanographers like Hiro Asahi who study the history of the oceans analyse these chemical components and draw conclusions about the character of past ocean currents.

View under the microscope: Planktic foraminifera (the white grains 
 in the picture) tell about ocean temperatures during the past. Certain 
species prefer certain temperature ranges. (photo: Kirstin Werner/
Steffen Aagaard Sørensen)

Eventually you make a cool story

Unlike most of his colleagues who investigate fossil foraminifera shells uncovered from the ocean floor, Hirofumi Asahi initially worked with those foraminifera that today live in the ocean. He studied the seasonal differences of foraminifers in the Bering Sea and the central Pacific: “We collected them from the upper water layers in large containers, so-called sediment traps, that were anchored in the deep ocean.” During his dissertation at Kyushu University Asahi determined the monthly foraminifera abundance and species composition in the sediment traps. In addition, he measured the ratio of oxygen isotopes in their calcite shells. Different isotopes of oxygen in foraminiferal calcite provide information on temperature and salinity of the surrounding water. As a second step, Asahi related his results from foraminifera geochemistry to the measured temperatures and salinities of the actual surrounding waters. For comparing modern water conditions with the characteristics of living planktic foraminifera is crucial for paleoceanographers. “First, we need to find about the relationship of foraminifera and the ocean currents in which they drift. Since the calcite of their shells is produced biologically, the translation of their chemical properties into temperature and salinity often is not straightforward. Our task is to find a systematic behind”, Asahi says. Only then fossilized foraminifers can be used to draw conclusions about former seawater conditions. “Once you spent some time at the microscope it becomes really interesting. In samples from the sediment traps you will always see a peak of foraminifer abundance in spring and in fall. Which can be explained by the nutrient supply from the bottom water. Kind of obvious to see that. But sometimes, you see some irregular stuff, and if you then for example find a bloom on the satellite photo taken from above your study region during exactly the time you ran your sediment trap study, you are really getting into the thing. You are like, ‘Oh that could be a nutrient!’ Or ‘Some kind of water mass stratification must have been strong’. Eventually you are able to connect the things to each other and make a cool story out of it. That is the thing I really like about my micropaleontology work!”

The history of the oceans during thousands of years is archived in marine 
sediments. Changes in colours are evidence of changing ocean conditions 
during the past. Marine geologists study microfossils preserved in the 
sediments.

Professor Takahashi, I'll be good!

As for many scientists for Hiro Asahi the time after his PhD studies was not easy. For several years he worked at the University of Tokyo but poorly paid. The telephone call of his PhD supervisor Kozo Takahashi some time during fall 2007 was thus a real surprise. “He was looking for a candidate that could join his international ocean drilling expedition into the Bering Sea. He said, ‘Are you sure you can do some work?’  Because at that time I even started to regret myself becoming a scientist since I couldn’t find a proper job. He also said, ‘I am sure you are pretty much interested in going on that cruise but I am a bit concerned about the low publication record you have so far.’” The very few, much sought-after spaces on an IODP (short for International Ocean Drilling Program) expedition are reserved for those scientists who publish their results as quickly as possible. “He was right”, Hiro admits, “At that moment I didn’t have that much publications out but I really wanted to go, so I told him: ‘Prof. Takahashi, forget about my past, I will be good!’”

During the IODP cruise the geological 
samples are directly viewed under the 
microscope. (photo: Hirofumi Asahi)

The IODP expedition aboard the US research vessel JOIDES Resolution into the Bering Sea has left a huge mark on Asahi’s scientific future: “The cruise was a complete turning point. Only since then I actually consider myself a real scientist. The quality of sediment cores was great, there were so many variations in colour that already told us on board about the stories of the past. That was really motivating.” In shifts, Asahi and his colleagues spent twelve hours a day working on the vessel for about two months in summer 2009. “We really became friends aboard. It was like a snap. Every hour a new core section came up. The technicians opened the core by splitting the plastic tubes with the fresh marine sediments inside into two halves. Our job was to view the sediments and write down what we saw.” For every centimetre of the 745 meters of sediment Asahi and his teammates noted the different colours and the grain sizes, the type of minerals and sometimes even the smell of the freshly recovered material collected from the seabed. “And then we waited again, sometimes twenty minutes, sometimes an hour until the next core came on deck.”

2.5 million years old foraminifers

Silently the sand trickles from the glass vial through the fine-meshed sieve. The hands tap gently against the frame of the sieve to separate the fine from the coarser sand. From here the coarse fraction of the sieved sand is poured into a porcelain dish. The sand is then brushed into a small metal bucket. Metal clicks on metal when the sample is divided into halves by the sample splitter. Dividing the sample is done as long as it needs to acquire a countable but more important statistically significant amount of foraminifers in a sample, usually this is about at least three hundred specimens. The counted foraminifera are later extrapolated onto the total amount of foraminifers in the sample.

Since the 1980s, satellites record daily sea-ice conditions 

in the Arctic. The sea-ice decrease also impacts the global climate.

Since the IODP expedition Asahi not only works with modern foraminifera but uses his knowledge about them especially for his paleoceanographic work. “Even before the expedition I used to work with geological material. But to be honest, it wasn’t very interesting to me just because there was no foraminifera in the samples.” In contrast, the material from the Bering Sea contains well-preserved foraminifer shells as old as 2.5 millions of years. “I personally believe that the Bering Strait had a great influence on the Bering Sea history. For the same reason I am curious about what had happened further north in the Arctic at the same time.” Changes in the Arctic affect the global climate. Since the 1980s, the Arctic sea ice significantly declined. Looking into the past of the Arctic may help to understand how the Arctic Ocean will behave in the future. “In order to do so we actually need another long and well-dated sediment core from the central Arctic. I would so much like to be there when such a core is drilled hopefully in the near future”, Hiro says. “Age control in Arctic geological sediment cores is the biggest problem because in the Arctic. Marine sediments often do not contain any foraminifer carbonate material which can be used for determining the age of the sediments.” In spring 2012, the now fourty-one year old Japanese moved to South Korea. First, he worked at Pusan National University in the south of the country. In 2014, Asahi moved to the Korea Polar Research Institute KOPRI in Incheon near Seoul. Here he continues his work in the Bering Sea but also started to investigate sediment cores from the central Arctic. “At KOPRI an Arctic scientist faces great opportunities. I have access to many sediment samples from the central Arctic. This kind of work I could never do in Japan since we do not have such a nice Arctic research institute there.” There is a National Institute of Polar Research in Japan but most of their effort is heading to Antarctic. A new institute targeting the Arctic Ocean has been established in Japan recently, yet they have no geology program included. Even though Asahi sometimes feels like eventually returning to Japan, as the work can be lonely at KOPRI. “I have no one to really discuss my data. Since I am so specialized, nobody does something similar.”

Cautiously the tiny tip of the needle taps and turns the white calcite package. An opening on the right side of the package becomes visible. Planktic foraminifera are growing chamber by chamber with the youngest chamber leaving an opening, called the aperture. Amongst other taxonomic identifiers the aperture helps in distinguishing between foraminifer species. “Far to the north, we do not have so many different foraminifer species. The most common one is the left-coiling type of Neogloboquadrina pachyderma. It loves the cool and salty waters”, Asahi explains. “These are present in countless numbers in the Arctic and in the Bering Sea. But every now and then I also see other types who like to have it a little warmer.” After so many years working with planktic foraminifera Asahi still remains curious: “I know that foraminifera cannot think. But I sometimes really wonder how they manage to produce these fantastic shapes.”