A global seasonal surface ocean climatology of phytoplankton types based on CHEMTAX analysis of HPLC pigments

Much advancement has been made in recent years in field data assimilation, remote sensing and ecosystem modeling, yet our global view of phytoplankton biogeography beyond chlorophyll biomass is still a cursory taxonomic picture with vast areas of the open ocean requiring field validations. High performance liquid chromatography (HPLC) pigment data combined with inverse methods offer an advantage over many other phytoplankton quantification measures by way of providing an immediate perspective of the whole phytoplankton community in a sample as a function of chlorophyll biomass. Historically, such chemotaxonomic analysis has been conducted mainly at local spatial and temporal scales in the ocean. Here, we apply a widely tested inverse approach, CHEMTAX, to a global climatology of pigment observations from HPLC. This study marks the first systematic and objective global application of CHEMTAX, yielding a seasonal climatology comprised of ~1500 1°x1° global grid points of the major phytoplankton pigment types in the ocean characterizing cyanobacteria, haptophytes, chlorophytes, cryptophytes, dinoflagellates, and diatoms, with results validated against prior regional studies where possible. Key findings from this new global view of specific phytoplankton abundances from pigments are a) the large global proportion of marine haptophytes (comprising 32 ± 5% of total chlorophyll), whose biogeochemical functional roles are relatively unknown, and b) the contrasting spatial scales of complexity in global community structure that can be explained in part by regional oceanographic conditions. These publicly accessible results will guide future parameterizations of marine ecosystem models exploring the link between phytoplankton community structure and marine biogeochemical cycles.

Chemical characterization and quantification of the brown algal storage compound laminarin

In search of a meaningful stress indicator for Fucus vesiculosus we found that the often used quantitative determination procedures for the polysaccharide laminarin (beta-1,3-glucan) result in different kind of problems, uncertainties and limitations. This chemical long-term storage form of carbon enables perennial brown algae in seasonally fluctuating ecosystems to uncouple growth from photosynthesis. Because of this high ecological relevance a reliable and precise method for determination and quantification of laminarin is needed. Therefore, a simple, cold water extraction method coupled to a new quantitative liquid chromatography-mass spectrometrical method (LC-MS) was developed. Laminarin was determined in nine out of twelve brown algal species, and its expected typical molar mass distribution of 2000-7000 Da was confirmed. Furthermore, laminarin consisted of a complex mixture of different chemical forms, since fifteen chemical laminarin species with distinct molecular weights were measured in nine species of brown algae. Laminarin concentrations in the algal tissues ranged from 0.03 to 0.86% dry weight (DW). The direct chemical characterization and quantification of laminarin by LC-MS represents a powerful method to verify the biochemical and ecological importance of laminarin for brown algae. Single individuals of Laminaria hyperborea, L. digitata, Saccharina latissima, F. serratus, F. vesiculosus, F. spiralis, Himanthalia elongata, Cystoseira tamariscifolia, Pelvetia canaliculata, Ascophyllum nodosum, Halidrys siliquosa and Dictyota dichotoma were collected in fall (18.11.2013) during spring low tide from the shore of Finavarra, Co. Clare, west coast of Ireland (53° 09' 25'' N, 09° 06' 58'' W). After sampling, the different algae were immediately transported to the lab, lyophilized and sent to the University of Rostock. Laminarin was extracted with cold ultrapure water from the algal samples. Before extraction they were ground to < 1 mm grain size with an analytical mill (Ika MF 10 Basic). The algal material (approx. 1.5 g DW) was extracted in ultrapure water (8 mL) on a shaker (250 rpm) for 5 h. After the addition of surplus ultrapure water (4 mL) and shaking manually, 1 mL of the sample was filter centrifuged (45 µm) at 14,000 rpm (Hettich Mikro 22 R). The slightly viscous supernatant was free of suspended material and converted into a microvial (300 µL) for further analysis. The extracts were analyzed using liquid chromatography-mass spectrometry (LC-MS) analysis (LTQ Velos Pro ion trap spectrometer with Accela HPLC, Thermo Scientific). Laminarin species were separated on a KinetexTM column (2.6 µm C18, 150 x 3 mm). The mobile phase was 90 % ultrapure water and 10 % acetonitrile, run isocratically at a flow rate of 0.2 mL min-1. MS was working in ESI negative ion mode in a mass range of 100 - 4000 amu. Glucose contents were determined after extraction using high-performance liquid chromatography (HPLC). Extracted samples were analyzed in an HPLC (SmartLine, Knauer GmbH) equipped with a SUPELCOGELTM Ca column (30 x 7,8 mm without preColumn) and RI-detector (S2300 PDA S2800). Water was used as eluent at a flow rate of 0.8 mL min-1 at 75 °C. Glucose was quantified by comparison of the retention time and peak area with standard solutions using ChromGate software. Mannitol was extracted from three subsamples of 10-20 mg powdered alga material (L. hyperborea, L. digitata, S. latissima, F. serratus, F. vesiculosus, F. spiralis, H. elongata, P. canaliculata, A. nodosum, H. siliquosa) and quantified, following the HPLC method described by Karsten et al. (1991). For analyzing carbon and nitrogen contents, dried algal material was ground to powder and three subsamples of 2 mg from each alga thalli were loaded and packed into tin cartridges (6×6×12 mm). The packages were combusted at 950 °C and the absolute contents of C and N were automatically quantified in an elemental analyzer (Elementar Vario EL III, Germany) using acetanilide as standard according to Verardo et al. (1990).

Contiunous surface water uncorrected and quench-corrected active fluorescence and derived chlorophyll a concentration using calibration by HPLC pigments during POLARSTERN cruise ANT-XXV/1

The relationship between phytoplankton assemblages and the associated optical properties of the water body is important for the further development of algorithms for large-scale remote sensing of phytoplankton biomass and the identification of phytoplankton functional types (PFTs), which are often representative for different biogeochemical export scenarios. Optical in-situ measurements aid in the identification of phytoplankton groups with differing pigment compositions and are widely used to validate remote sensing data. In this study we present results from an interdisciplinary cruise aboard the RV Polarstern along a north-to-south transect in the eastern Atlantic Ocean in November 2008. Phytoplankton community composition was identified using a broad set of in-situ measurements. Water samples from the surface and the depth of maximum chlorophyll concentration were analyzed by high performance liquid chromatography (HPLC), flow cytometry, spectrophotometry and microscopy. Simultaneously, the above- and underwater light field was measured by a set of high spectral resolution (hyperspectral) radiometers. An unsupervised cluster algorithm applied to the measured parameters allowed us to define bio-optical provinces, which we compared to ecological provinces proposed elsewhere in the literature. As could be expected, picophytoplankton was responsible for most of the variability of PFTs in the eastern Atlantic Ocean. Our bio-optical clusters agreed well with established provinces and thus can be used to classify areas of similar biogeography. This method has the potential to become an automated approach where satellite data could be used to identify shifting boundaries of established ecological provinces or to track exceptions from the rule to improve our understanding of the biogeochemical cycles in the ocean.

Microphytobenthos composition in Heron Reef, Australia, by High Performance Liquid Chromatography (HPLC) (July 2012)

We quantified pigment biomarkers by high performance liquid chromatography (HPLC) to obtain a broad taxonomic classification of microphytobenthos (MPB) (i.e. identification of dominant taxa). Three replicate sediment cores were collected at 0, 50 and 100 m along transects 5-9 in Heron Reef lagoon (n=15) (Fig. 1). Transects 1-4 could not be processed because the means to have the samples analysed by HPLC were not available at the time of field data collection. Cores were stored frozen and scrapes taken from the top of each one and placed in cryovials immersed in dry ice. Samples were sent to the laboratory (CSIRO Marine and Atmospheric Research, Hobart, Australia) where pigments were extracted with 100% acetone during fifteen hours at 4°C after vortex mixing (30 seconds) and sonication (15 minutes). Samples were then centrifuged and filtered prior to the analysis of pigment composition with a Waters - Alliance HPLC system equipped with a photo-diode array detector. Pigments were separated using a Zorbax Eclipse XDB-C8 stainless steel 150 mm x 4.6 mm ID column with 3.5 µm particle size (Agilent Technologies) and a binary gradient system with an elevated column temperature following a modified version of the Van Heukelem and Thomas (2001) method. The separated pigments were detected at 436 nm and identified against standard spectra using Waters Empower software. Standards for HPLC system calibration were obtained from Sigma (USA) and DHI (Denmark).

Intact and core tetraether lipids in water column profiles of suspended particulate matter and of surface sediment samples off Cape Blanc, NW Africa

In the reconstruction of sea surface temperature (SST) from sedimentary archives, secondary sources, lateral transport and selective preservation are considered to be mainly negligible in terms of influencing the primary signal. This is also true for the archaeal glycerol dialkyl glycerol tetraethers (GDGTs) that form the basis for the TEX86 SST proxy. Our samples represent four years variability on a transect off Cape Blanc (NW Africa). We studied the subsurface production, vertical and lateral transport of intact polar lipids and core GDGTs in the water column at high vertical resolution on the basis of suspended particulate matter (SPM) samples from the photic zone, the subsurface oxygen minimum zone (OMZ), nepheloid layers (NL) and the water column between these. Furthermore we compared the water column SPM GDGT composition with that in underlying surface sediments. This is the first study that reports TEX86 values from the precursor intact polar lipids (IPLs) associated with specific head groups (IPL -specific TEX86). We show a clear deviation from the sea surface GDGT composition in the OMZ between 300 and 600 m. Since neither lateral transport nor selective degradation provides a satisfactory explanation for the observed TEX-derived temperature profiles with a bias towards higher temperatures for both core- and IPL -specific TEX86 values, we suggest that subsurface in situ production of archaea with a distinct relationship between lipid biosynthesis and temperature is the responsible mechanism. However, in the NW-African upwelling system the GDGT contribution of the OMZ to the surface sediments does not seem to affect the sedimentary TEX86 as it shows no bias and still reflects the signal of the surface waters between 0 and 60 m.