ALBERT

Description: Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles. More than 96% of the marine DOM resists microbial degradation for thousands of years. The composition of this refractory DOM (RDOM) exhibits a molecular signature which is ubiquitously detected in the deep oceans. Surprisingly efficient microbial transformation of labile into RDOM was shown experimentally, implying that microorganisms produce far more RDOM than needed to sustain the global pool. By assessing the microbial formation and transformation of DOM in unprecedented molecular detail for 3 years, we show that most of the newly formed RDOM is molecularly different from deep sea RDOM. Only 〈0.4% of the net community production was channeled into RDOM molecularly undistinguishable from deep sea DOM. Our study provides novel experimentally derived molecular evidence and data for global models on the production, turnover and accumulation of marine DOM.

Description: Dissolved organic matter (DOM) is the main substrate and energy source for heterotrophic bacterioplankton. To understand the interactions between DOM and the bacterial community (BC), it is important to identify the key factors on both sides in detail, chemically distinct moieties in DOM and the various bacterial taxa. Next-generation sequencing facilitates the classification of millions of reads of environmental DNA and RNA amplicons and ultrahigh-resolution mass spectrometry yields up to 10,000 DOM molecular formulae in a marine water sample. Linking this detailed biological and chemical information is a crucial first step toward a mechanistic understanding of the role of microorganisms in the marine carbon cycle. In this study, we interpreted the complex microbiological and molecular information via a novel combination of multivariate statistics. We were able to reveal distinct relationships between the key factors of organic matter cycling along a latitudinal transect across the North Sea. Total BC and DOM composition were mainly driven by mixing of distinct water masses and presumably retain their respective terrigenous imprint on similar timescales on their way through the North Sea. The active microbial community, however, was rather influenced by local events and correlated with specific DOM molecular formulae indicative of compounds that are easily degradable. These trends were most pronounced on the highest resolved level, that is, operationally defined 'species', reflecting the functional diversity of microorganisms at high taxonomic resolution.

Description: Two bacterial species members of the Roseobacter group (P. inhibens and D. shibae) were cultivated using three different substrates as a sole carbon source. The molecular fingerprint of the medium was analyzed at three different time points corresponding to the lag, exponential and stationary growth phases. North equatorial pacific intermediate water was also measured in replicates. This water mass represents one of the oldest water masses in our oceans and it is therefore used as a representative for refractory dissolved organic matter. Data includes mass, molecular formula (if available) and relative intensity normalized to 100%

Description: We assessed relationships between phytoplankton standing stock, measured as chlorophyll a (Chl a), primary production (PP), and heterotrophic picoplankton production (HPP), in the epipelagic zone (0-100 m) as well as in the mesopelagic zone (100-1,000 m) in the polar frontal zone of the Atlantic sector of the Southern Ocean in austral summer (late December to January) and fall (March to early May). Integrated epipelagic HPP was positively correlated to integrated PP in summer (data for fall are not available) but not to integrated Chl a. However, integrated mesopelagic HPP was positively correlated to Chl a in summer as well as fall. The mesopelagic fraction of HPP as a percentage of total HPP was also positively correlated to Chl a, whereas the epipelagic fraction of HPP was negatively correlated to it. These results indicate that with increasing phytoplankton standing stock, constituted mainly of highly silicified diatoms, the focus of its consumption by heterotrophic picoplankton shifts from epipelagic to mesopelagic waters. With a growth efficiency of 30%, our HPP data indicate that in both the epipelagic and mesopelagic zone heterotrophic picoplankton consume 20% of PP. Mesopelagic heterotrophic picoplankton consumed around 80% of the sinking flux, measured from depletion of 234Th, which is a lower fraction than that reported from the central and subarctic Pacific. Our analysis indicates that it is important to include mesopelagic HPP in comprehensive assessments of the microbial consumption of PP, phytoplankton biomass, and particulate organic matter in cold oceanic systems with high rates of export production.

Description: The data presented here were collected during the cruise SO248 (Project BacGeoPac) with the RV Sonne from Auckland, New Zealand to Dutch Harbor, Alaska/USA. The cruise lasted from May 1, 2016 to June 3, 2016 and 19 vertical CTD-hauls were conducted. The CTD system used during this cruise was a Sea-Bird Electronics Inc. SBE 911plus probe (SN 09-1266). The CTD was attached to a SBE 32 Carousel Water Sampler (SN 32-1119) containing 24 20-liter Ocean Test Equipment Inc. bottles. The system was equipped with double temperature (SBE 3) and conductivity sensors (SBE 4), a pressure sensor (Digiquartz) an oxygen (Aanderaa Optode 4831F) and, an altimeter (Bentos) and a chlorophyll fluorometer combined with a turbidity sensor (FluoroWetlabECO _AFL FL). The sensors were pre-calibrated by the manufacturers. The data were recorded with the Seasave V 7.23.2 software and processed using the SeaBird SBE Data Processing and the ManageCTD-software. The data were processed in the following way: Data obtained during adaptation of the CTD to ambient water conditions were removed manually. The “wildedit”, “loopedit”, “despike”, “binavg” routines were applied. The data were also visually checked and a double sensor check was conducted. The accuracy of the double sensors derived from 56 data sets were: Temperature T = 0.0007 °C; Conductivity: C = 0,0071 mS/cm; Salinity S = 0.0081 psu. The salinity data (S by unsing pss78) were converted to absolute Salinity (SA) by using the TEOS 10 toolbox. The ship position data were derived from the shipboard GPS-system linked to the CTD data. The time zone is given in UTC. The oxygen CTD data were validated by additional measurements of 98 water samples using the Winkler titration method.

Description: To investigate links between biological, biogeochemical and physical parameters, we closely monitored an artificially induced spring bloom. Our mesocosm approach mimicked a neritic North Sea water body. Three biological replicates (P2-P4) were inoculated with a phytoplankton and associated bacterial community, which was retrieved in March 2018 from the southern North Sea. The incubation was monitored for 38 days. The experiment additionally covered the investigation of two biota-free controls. A variety of parameters were sampled, the results of some can be found in Mori et al. (2021; doi:10.1016/j.gca.2021.08.002). Total alkalinity was sampled daily. For the analysis we used a multiscan GO microplate spectrophotometer (Thermo Scientific) and followed the method described by Sarazin et al. (1999; doi:10.1016/S0043-1354(98)00168-7).