ALBERT

Description: The copepod Calanus finmarchicus plays a crucial role in the north Atlantic food web. Its seasonal life cycle involves reproduction and development in surface waters before overwintering in diapause at depth. Although diapause has been studied for more than a century, the factors responsible for the initiation and termination of it are still unclear. Endogenous clocks have been identified as potent tools for photoperiod measurement and seasonal rhythmicity in many terrestrial species, but knowledge of these remains scarce in the marine realm. Focusing on the dominant CV copepodid stage, we sampled a population of C. finmarchicus from a Scottish sea loch to characterize population dynamics, several physiological parameters, and diel and seasonal expression rhythms of 35 genes representing different metabolic pathways, including the circadian clock machinery. This generated a detailed overview of the seasonal cycle of C. finmarchicus including the most extensive field dataset on circadian clock gene expression in a marine species to date. Gene expression patterns revealed distinct gene clusters upregulated at different phases of the copepod's seasonal cycle. While diel clock cycling was restricted to the active spring/summer phase, many clock genes exhibited the highest expression during diapause. Our results provide new insights into diapause on physiological and genetic levels. We suggest that photoperiod, in interaction with internal and external factors (lipid content, temperature, food availability) and the endogenous clock mechanism, plays an important role in the timing of diapause in C. finmarchicus.

Description: Branched glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of unknown bacteria that are ubiquitous in soil and peat. Two indices based on the distribution of these lipids in soils, the Cyclization of Branched Tetraethers (CBT) and the Methylation of Branched Tetraethers (MBT) indices have been shown to correlate with soil pH, and mean annual air temperature (MAT) and soil pH, respectively, and can be used to reconstruct MAT in palaeoenvironments. To verify the extent to which branched GDGTs in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a MAT of 〈0 °C, we compared the branched GDGT distribution in Svalbard soils and nearby fjord sediments. Although branched GDGT concentrations in the soil are relatively low (0.02-0.95 µg/g dry weight (dw)) because of the cold climate and the short growing season, reconstructed MATs based on the MBT/CBT proxy are ca. -4 °C, close to the measured MAT (ca. -6 °C). Concentrations of branched GDGTs (0.01-0.20 µg/g dw) in fjord sediments increased towards the open ocean and the distribution was strikingly different from that in soil, i.e. dominated by GDGTs with one cyclopentane moiety. This resulted in MBT/CBT-reconstructed MAT values of 11- 19 °C, well above measured MAT. The results suggest that at least part of the branched GDGTs in marine sediments in settings with a low soil organic matter (OM) input may be produced in situ. In these cases, the application of the MBT/CBT palaeothermometer will generate unrealistic MAT reconstructions. The MBT/CBT proxy should therefore only be used at sites with a substantial input of soil OM relative to the amount of marine OM, i.e. at sites close to the mouth of rivers with a catchment area where sufficient soil formation takes place and the soil thus contains substantial amounts of branched GDGTs.

Description: Long chain alkyl diols are lipids that occur ubiquitously in marine sediments and are used as a proxy for sea surface temperature (SST), using the Long chain Diol Index (LDI), and for upwelling intensity/high nutrient conditions. The distribution of 1,13- and 1,15-diols has been documented in open marine and lacustrine sediments and suspended particulate matter, but rarely in coastal seas receiving a significant riverine, and thus continental organic matter, input. Here we studied the distribution of diols in four shelf seas with major river outflows: the Gulf of Lion, the Kara Sea, the Amazon shelf and the Berau delta, covering a wide range of climate conditions. The relative abundance of the C32 1,15-diol is consistently higher close to the river mouth and particularly in the suspended particulate matter of the rivers suggesting a terrigenous source. This is supported by statistical analysis which points out a significant positive correlation between the C32 1,15-diol and the Branched and Isoprenoid Tetraether index, a proxy reflecting soil and riverine input in marine environments. However, the C32 1,15-diol was not detected in soils and is unlikely to be derived from vegetation, suggesting that the C32 1,15-diol is mainly produced in rivers. This agrees with the observation that it is a dominant diol in most cultivated freshwater eustigmatophyte algae. We, therefore, suggest that the relative abundance of the C32 1,15-diol can potentially be used as a proxy for riverine organic matter input in shelf seas. Our results also show that long chain alkyl diols delivered by rivers can substantially affect LDI-reconstructed SSTs in coastal regions close to river mouths.

Description: There is increasing evidence that nitrifying Thaumarchaeota in the deep ocean waters may contribute to the sedimentary composition of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs), impacting TEX86 paleothermometry. We inves- tigated the potential effect of deep-water dwelling Thaumarchaeota in the warm and saline Mediterranean Outflow Water (MOW) on the distribution of isoGDGTs by analysing suspended particulate matter (SPM) and surface sediments collected along five land-ocean transects along the southern Portuguese continental margin. To this end, we directly compared for the first time the composition of intact polar lipid (IPL)-derived isoGDGTs of SPM with the diversity, abundance, and activity of Thaumarchaeota based on the genetic analysis of the genes coding for the archaeal ammonia monooxygenase (amoA) and the geranylgeranylglyceryl phosphate (GGGP) synthase involved in the isoGDGT biosynthetic pathway. Our results revealed a strong positive relationship between water depth and TEXH86 values for both SPM and surface sediments. The increasing TEXH86 trends for both core lipid (CL) and IPL-derived fractions were accompanied by increasing fractional abundances of GDGT-2 and crenarchaeol regio-isomer and decreasing fractional abundances of GDGT-1 and GDGT-3 with increasing water depth. Phylogenetic analyses based on the archaeal amoA and the GGGP synthase proteins showed that Thaumarchaeota populations detected at 1m and 50 m water depth were different from those detected in 200 m and 1000 m water depth, which had an increased contribution of so-called 'deep water' Thaumarchaeota. The differences in the fractional abundances of isoGDGTs with water depth were compatible with the increasing contribution of 'deep water' Thaumarchaeota harboring a different GGGP synthase enzyme which has been suggested to relate to changes in the relative proportion of synthesized isoGDGTs. Accordingly, it appears that the sedimentary distribution of CL isoGDGTs used in TEXH86 along the Portuguese margin is primarily influenced by water depth due to the increasing contribution of the deep-water population of Thaumarchaeota residing in the MOW. Our study also reveals that the effect of deep water Thaumarchaeotal communities on sedimentary isoGDGT distributions should be considered globally.

Description: In this study, we investigated soils and river suspended particulate matter (SPM) collected in the Rhône and its tributary basins as well as marine surface sediments taken in the Rhône prodelta (Gulf of Lions, NW Mediterranean). Thereby, we traced the signal of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from the source to sink via the Rhône River and its tributaries and identified sources of brGDGTs in rivers and marine sediments. Soil pH rather than the mean annual air temperature (MAAT) explains most of the observed variances of the brGDGT distribution in our soil dataset. The observed changes in the distribution of brGDGTs in the river SPM indicate that brGDGTs brought by the river to the sea are primarily derived from the lower Rhône and its tributary soils, even though in situ production in the river itself cannot be excluded. In marine surface sediments, it appears that the input of riverine brGDGTs is the primary source of brGDGTs in the Rhône prodelta, although the brGDGT composition may be further modified by the in situ production in the marine environment. More work is required to assess fully whether brGDGTs can be used to reconstruct the terrestrial paleoenvironmental changes using marine sediment cores taken in the Rhône prodelta close to the river mouth.