Polarstern, 07°0´N, 23°48´W

The past week on the PS120 Transit between Port Stanley and Bremerhaven was characterised by a lot of sampling stations, especially at night with high seas. Many large birds accompanied us and dived for fish in our wake.

As we have a microplastic expert on board: Dr. Inga Kirstein from the AAU, Aalborg, in Denmark we were on the lookout for plastic debris. In the middle of last week we transversed the edge of an area which is known to be a type of plastic “gyre” and sure enough we  found plastic bags and bottles floating on the  surface. As this topic is so very important, I have asked Inga to write a piece on it for you here.

Microplastics on the SoNoAT Inga Vanessa Kirstein (AAU, Aalborg, Denmark)

Plastics represent the most rapidly growing form of anthropogenic litter entering and accumulating in our oceans, and are therefore a growing threat for humans and nature. Most plastic types are poorly degradable in the marine environment. They become brittle and subsequently break down in small particles, so called microplastics. Along the SoNoAT expedition track between Port Stanley and Bremerhaven we take sub-surface water samples via an underway water intake system of the POLARSTERN in order to address the abundance, distribution, and composition of microplastics. Two sampling procedures are carried out. Firstly, at the sampling stations, seawater was filtered directly through 10 µm stainless steel filters in a closed steel filter system to prevent contamination and aim for small microplastics (< 20 µm). Secondly, on a daily basis, seawater is filtered through geological sieves (bottom: 0.02 mm, centre: 0.2 mm and top: 0.3 mm mesh) enabling the filtration of a higher volume of water, as well as size fractionizing of the sample. All samples are stored at -20°C for later polymer analysis in the laboratory. After visual inspection on board there are no indications for microplastics (> 300 µm) in the samples. Since bigger plastic items are fragmented over time, we expect to find increasing amounts of microplastics with decreasing particle size. Therefore, collected microplastic samples will undergo sample preparation and subsequent characterization.

The ocean has become less rough in the past days. This might have to do with the fact that  Neptune and Thetis visited us. It's easier to see the drifting debris on the surface as well as flying fish and whales. At night one can stand on deck again and enjoy the stars without getting soaked by sea spray. Sending you the beauty of the ocean sky at night with best wishes to families, friends and colleagues.  

Karen Wiltshire