Spatial distribution of key zooplankton species using continuous plankton recorder (CPR) data from the North Atlantic (2000-2009)

The continuous plankton recorder (CPR) survey is an upper layer plankton monitoring program that has regularly collected samples, at monthly intervals, in the North Atlantic and adjacent seas since 1946. Water from approximately 6 m depth enters the CPR through a small aperture at the front of the sampler and travels down a tunnel where it passes through a silk filtering mesh of 270 µm before exiting at the back of the CPR. The plankton filtered on the silk is analyzed in sections corresponding to 10 nautical miles (approx. 3 m**3 of seawater filtered) and the plankton microscopically identified (Richardson et al., 2006 and reference therein). In the present study we used the CPR data to investigate the current basin scale distribution of C. finmarchicus (C5-C6), C. helgolandicus (C5-C6), C. hyperboreus (C5-C6), Pseudocalanus spp. (C6), Oithona spp. (C1-C6), total Euphausiida, total Thecosomata and the presence/absence of Cnidaria and the Phytoplankton Colour Index (PCI). The PCI, which is a visual assessment of the greenness of the silk, is used as an indicator of the distribution of total phytoplankton biomass across the Atlantic basin (Batten et al., 2003). Monthly data collected between 2000 and 2009 were gridded using the inverse-distance interpolation method, in which the interpolated values were the nodes of a 2 degree by 2 degree grid. The resulting twelve monthly matrices were then averaged within the year and in the case of the zooplankton the data were log-transformed (i.e. log10 (x+1).

Distribution of deep-sea foraminifera in surface sediments east of New Zealand

Paleobathymetric assessments of fossil foraminiferal faunas play a significant role in the analysis of the paleogeographic, sedimentary, and tectonic histories of New Zealand's Neogene marine sedimentary basins. At depths >100 m, these assessments often have large uncertainties. This study, aimed at improving the precision of paleodepth assessments, documents the present-day distribution of deep-sea foraminifera (>63 µm) in 66 samples of seafloor sediment at 90-700 m water depth (outer shelf to mid-abyssal), east of New Zealand. One hundred and thirty-nine of the 465 recorded species of benthic foraminifera are new records for the New Zealand region. Characters of the foraminiferal faunas which appear to provide the most useful information for estimating paleobathymetry are, in decreasing order of reliability: relative abundance of common benthic species; benthic species associations; upper depth limits of key benthic species; and relative abundance of planktic foraminifera. R mode cluster analysis on the quantitative census data of the 58 most abundant species of benthic foraminifera produced six species associations within three higher level clusters: (1) calcareous species most abundant at mid-bathyal to outer shelf depths (<1000 m); (2) calcareous species most abundant at mid-bathyal and greater depths (>600 m); (3) agglutinated species mostly occurring at deep abyssal depths (>3000 m). A detrended correspondence analysis ordination plot exhibits a strong relationship between these species associations and bathymetry. This is manifest in the bathymetric ranges of the relative abundance peaks of many of the common benthic species (e.g., Abditodentrix pseudothalmanni 500-2800 m, Bolivina robusta 200-650 m, Bulimina marginata f. marginata 20-600 m, B. marginata f. aculeata 400-3000 m, Cassidulina norvangi 1000-4500 m, Epistominella exigua 1000-4700 m, and Trifarina angulosa 10-650 m), which should prove useful in paleobathymetric estimates. The upper depth limits of 28 benthic foraminiferal species (e.g., Fursenkoina complanata 200 m, Bulimina truncana 450 m, Melonis affinis 550 m, Eggerella bradyi 750 m, and Cassidulina norvangi 1000 m) have potential to improve the precision of paleobathymetric estimates based initially on the total faunal composition. The planktic percentage of foraminiferal tests increases from outer shelf to upper abyssal depths followed by a rapid decline within the foraminiferal lysocline (below c. 3600 m). A planktic percentage <50% is suggestive of shelf depths, and >50% is suggestive of bathyal or abyssal depths above the CCD. In the abyssal zone there is dramatic taphonomic loss of most agglutinated tests (except some textulariids) at burial depths of 0.1-0.2 m, which negates the potential usefulness of these taxa in paleobathymetric assessments.

Spatial and seasonal distribution of Thaumarchaeota in the water column and sediment of the southern North Sea

We have examined the spatial and seasonal distribution of Thaumarchaeota in the water column and sediment of the southern North Sea using the specific intact polar lipid (IPL) hexose, phosphohexose (HPH) crenarchaeol, as well as thaumarchaeotal 16S rRNA gene abundances and expression. In the water column, a higher abundance of Thaumarchaeota was observed in the winter season than in the summer, which is in agreement with previous studies, but this was not the case in the sediment where Thaumarchaeota were most abundant in spring and summer. This observation corresponds well with the idea that ammonia availability is a key factor in thaumarchaeotal niche determination. In the surface waters of the southern North Sea, we observed a spatial variability in HPH crenarchaeol, thaumarchaeotal 16S rRNA gene abundance and transcriptional activity that corresponded well with the different water masses present. In bottom waters, a clear differentiation based on water masses was not observed; instead, we suggest that observed differences in thaumarchaeotal abundance with depth may be related to resuspension from the sediment. This could be due to suspension of benthic Thaumarchaeota to the water column or due to delivery of e.g. resuspended sediment or ammonium to the water column, which could be utilized by pelagic Thaumarchaeota. This study has shown that the seasonality of Thaumarchaeota in water and sediment is different and highlights the importance of water masses, currents and sedimentary processes in determining the spatial abundance of Thaumarchaeota in the southern North Sea.

Compilation of organic carbon distribution and sedimentology in the surface sediments on the continental margin offshore southwestern Africa

In this study we demonstrate the relevance of lateral particle transport in nepheloid layers for organic carbon (OC) accumulation and burial across high-productive continental margins. We present geochemical data from surface sediments and suspended particles in the bottom nepheloid layer (BNL) from the most productive coastal upwelling area of the modern ocean, the Benguela upwelling system offshore southwest Africa. Interpretation of depositional patterns and comparison of downslope trends in OC content, organic matter composition, and 14C age between suspended particles and surface sediments indicate that lateral particle transport is the primary mechanism controlling supply and burial of OC. We propose that effective seaward particle transport primarily along the BNL is a key process that promotes and maintains local high sedimentation rates, ultimately causing high preservation of OC in a depocenter on the upper slope offshore Namibia. As lateral transport efficiently displaces areas of enhanced OC burial from maximum production at highly productive continental margins, vertical particle flux models do not sufficiently explain the relationship between primary production and shallow-marine OC burial. On geologic time scales, the widest distribution and strongest intensity of lateral particle transport is expected during periods of rapid sea-level change. At times in the geologic past, widespread downslope lateral transport of OC thus may have been a primary driver of enhanced OC burial at deeper continental slopes and abyssal basins.