The UK-based project Changes of the Arctic Ocean Seafloor (ChAOS) joined the last Nansen Legacy research cruise with two scientists from the University of Leeds, UK. Mark Zindorf and Allyson Tessin describe their work and motivation to join the Nansen Legacy cruise.
The life at the seafloor receives a constant supply of food. It trickles down as marine snow, which consists of all the material which is produced in the upper, sunlit layers of the ocean: algae, fish-fecals, decayed animals and so on. About 98% of the produced material is consumed by organisms living in the water column and only the remaining few percent reach the seafloor. But this is still enough to support a variety of seafloor organisms, including a consortium of microorganisms.
Vast areas of the Arctic Ocean are covered year-round by a thick ice cover. This limits the production of organic matter underneath and thus the transport of organic material to the seafloor. Currently global climate change leads to a shrinking in ice cover in the arctic, leaving areas ice free that have previously constantly been covered by ice. In ice free waters more algae can grow and produce more organic material which is deposited at the seafloor. Thus, climate change can lead to less sea ice and an increased supply of organic material to the seafloor, potentially supplying more organisms with food. However, these organisms will use more oxygen when they digest this additional food, which starves of oxygen organisms on the seafloor. Thus, a changing climate will have a direct effect on communities of microbes which have developed in the mud of the seafloor over the course of millennia.
The British ChAOS project abbreviation stands for Changes of the Arctic Ocean Seafloor, and investigates the effect past and future climate changes have on the seafloor communities and their food sources. Thus, the aims of ChAOS and Nansen Legacy link up perfectly. For this reason, we joined the Nansen Legacy Paleocruise 2018 to investigate this interesting subject on the same sites investigated by the Nansen Legacy.
On this cruise, we extract water from the marine mud from the drilled sediment cores. The chemical composition of these sedimentary pore-waters reflects the living conditions of the life in the seafloor. To avoid destruction of the sediment record, the pore-water sampling is done in a similar way as plant-roots extract water from soil.
A rhizon, a filter-tube with a very small pore size, is inserted into the sediment and the water is sucked out by a vacuum created with a common syringe. In these pore-waters products of microbial organic matter degradation, as well as nutrients are analyzed and compared between different drill sites which are temporarily or year-round ice covered, or have recently become ice-free. By this, predictions can be made on how the decreasing ice cover will affect the turn-over of organic material in the seafloor and how life, especially microbial life will be living in the future.
ChAOS and The Nansen Legacy have an active collaboration, with an engaging information and data exchange. The two projects also do participate in each other’s project meetings, student exchange and participate in each other’s cruises.