The scientific activities of cruise MSM-79 focus on “organic carbon" and processes that steer its turnover. Despite that it is well known that carbon dioxide is an important greenhouse gas affecting our climate and that the ocean plays an important role in the global carbon cycle, many key processes regarding the entry/production, transport, deposition and degradation of organic carbon to and at the ocean floor as well as the carbon re-emission to the atmosphere, are not well understood.
During this cruise we investigated several of these “key aspects” during two legs. The second Leg MACPEI (Las Palmas – Mindelo), investigated the now active processes of production and entry of organic carbon in the ocean as well as on its transport through the water column and its degradation. So called “old carbon” and the process of thawing of permafrost soils, staid in the spotlight of our first leg EUROTHAW (Edinburgh – Las Palmas).
Thawing of permafrost soils is currently taking place in large parts of Siberia and northern North America as a result of today's global warming. It can release large amounts of old carbon, much of which enters the ocean via river systems.
This process has occurred more often in the earth history with the previous event occurring at the end of last ice age that ended about 20.000 years ago. At that time, large parts of Europe were covered by ice sheets, while the non-ice-covered ground was largely permanently frozen (Figure 3.1). The ice sheets were drained by a huge river system which discharge waters flowed into the Atlantic Ocean. The river mouth of this palaeo-river was located in today's Bay of Biscay at the entrance of the English Channel.
To study the impact of this release on marine ecosystems and the processes leading to the degradation and/or deposition of this carbon as well as the effects of this release on the global climate, high-resolution sediment archives that record this melting of European permafrost have been obtained after studying the ocean floor morphology and its subsurface sediment with Parasound and Multibeam. The exact age and origin region of the collected “thawed organic carbon” will be investigated at the MARUM (Bremen) and AWI (Bremerhaven) with organic geochemical and palynological methods including compound-specific radiocarbon analyses with the MICADAS small scale accelerator mass spectrometer.
Research activities during Leg 2; the MACPEI program, aimed at obtaining a comprehensive insight into key aspects of the ocean carbon pump during active upwelling, notably mechanisms and processes that shape the vertical organic-matter particle flux, the turnover, transport, degradation and alteration of OM during the settling process and the effect of these processes on selected OM based palaeoceanographic lipid biomarker proxies.
For this, a comprehensive “ecosystem” approach was followed by studying the production, settling, degradation and alteration of organic matter in relationship to environmental and oceanographic properties, notably mineral dust input, upwelling intensity, redox conditions and the presence of nepheloid layers. Among this major representatives of the ecosystem (phytoplankton, zooplankton and microbial community) were followed from their production and activity in the water column towards embedding in the sediments.
Off Cape Blanc investigations concentrated on two transects: one transect that was placed along a drifting trap-track that followed the course of freshly upwelled waters over a period of 7 days, the second along an onshore-offshore transect covering the location of active upwelling towards the open ocean.
In order to investigate how bioproductivity, the plankton community and vertical particle flow change during the movement from the upwelled water masses, the upper water column waters were sampled using Rosette and membrane pump. Furthermore, drifting traps were deployed that collected the export flux of particles out of the surface waters at 100m, 200m, and 400m water depth. Using satellite records of water temperature, the exact location of an active upwelling cell was determined to locate the position of deployment of the first trap. Using the iridium satellite and VHF signals the trap was followed for 24 hours to be recovered and replaced by a second trap series. This continued for 7 days with the traps being replaced daily. Collected particles were investigated on the association of phytoplankton, coccolithophorids, dinoflagellate cysts and foraminifera as well as the presence of dust immediately after recovery. Furthermore selected POM particles were isolated and fixed at -20°C to be studied on their molecular composition and structure as well as compound specific age at the home institutes.
Scientific activities on the onshore-offshore transect focused on microbial formation and degradation of particulate organic matter (POM) with a known origin (coccolithophorids, dinoflagellate cysts and pollen/spores) under different redox conditions and in and between the nepheloid layers. Additionally the vertical and lateral transport as well a the effect of degradation processes on the association and composition of organic, calcareous and lithogenic particules (coccolithophorids, dinoflagellate cysts, foraminifera, lithogenic dust particles and pollen/spores) have been studied notably in relationship to the presence of nepheloid layers and different redox conditions.
Additionally the rate of metabolic activity of archaea and bacteria at different oxygen concentrations have been investigated during on board incubation experiments with bacteria and archaea with isotopically labeled inorganic and organic carbon sources. Hereby a quantification of the chemosynthesis rates of ammonia-oxidizing archaea in correlation with nitrification rates has been determined. Furthermore uptake mechanisms of characteristic amino acids in heterotrophic microorganisms have been studied. For this, bacteria and archaea consortia were collected within, along the margin and below the oxygen minimum zone using Rosette sampling.
Two dust collecting buoys (named "Carmen" and "Laura") and 4 sediment trap moorings were serviced (CB, CBi, M1 and a NIOZ test buoy). Dust collectors that had collected dust for one year at the same time intervals as the sediment trap moorings CB, CBi and M1.
Sediment traps CB and CBi are part of the long-term observation monitoring program of the MARUM that started in 1988. Sediment traps have been serviced on a yearly basis since.