Pw Boyd

A biogeochemical study of the coccolithophore, Emiliania huxleyi, in the North Atlantic

The biogeochemical properties of an extensive bloom (∼250,000 km2) of the coccolithophore, Emiliania huxleyi, in the north east Atlantic Ocean were investigated in June 1991. Satellite (NOAA-AVHRR) imagery showed that the bloom was centered initially at 60°–63°N by 13°–28°W and lasted approximately 3 weeks. Spatial variations in satellite-measured reflectance were well correlated with surface measurements of the beam attenuation coefficient, levels of particulate inorganic carbon, and coccolith density. Rates of both photosynthesis and calcification were typically relatively low within the coccolithophore-rich waters, suggesting the population was in a late stage of development at the time of the field observations. Levels of dimethyl sulphide (DMS) in surface waters were high compared to average ocean values, with the greatest concentrations in localized areas characterized by relatively high rates of photosynthesis, calcification, and grazing by microzooplankton. The estimated spatially averaged flux of DMS to the atmosphere was 1122 nmol m−2 h−1, somewhat greater than that determined for the same region in June-July 1987. Coccolith production (1 × 106 tonnes calcite-C) had a significant impact on the state of the CO2 system, causing relative increases of up to 50 μatm in surface pCO2 in association with alkalinity and water temperature changes. Gradients in pCO2 were as great as 100 μatm over horizontal distances of 20–40 km. The environmental implications of these findings are discussed in relation to the spatial and temporal distributions of E. huxleyi.

Water column and sea-ice primary production during Austral spring in the Bellingshausen Sea

Abstract The findings of a cruise to study the phytoplankton bloom dynamics associated with the marginal ice zone (MIZ) in the Bellingshausen Sea during Austral spring (November-December) 1992 are reported. Biomass and rate process measurements were carried out at stations located in the ice, ice edge and open water along the 85°W meridian in order to establish the productivity of the microalgae associated with sea-ice and in the water column. In addition, a series of transects along 85°W from sea-ice to open water conditions enabled an assessment of the development of phytoplankton populations. Low phytoplankton biomass and production were noted at ice-covered and ice-edge stations and in the open water close to the ice edge. Observations from the transects indicated no development of a classical ice edge bloom despite evidence that sea-ice had retreated more than 100 km during the study period. Survey data along the 85°W line revealed a region of high chlorophyll, centred on 67.5°S, which was initially observed during brash ice conditions. This feature, which remained geographically consistent, persisted for at least 25 days and was thought to be associated with a frontal region. Water column primary production ( 14 C) in this high chlorophyll region was ca 0.8 g C m −2 day − , more than 8 times higher than noted in the MIZ. Phytoplankton photosynthetic characteristics within this region indicated that cells were adapted to a low light regime. A critical depth of 80 m, estimated directly from oxygen flux measurements, was sufficient to permit the initiation and net growth of phytoplankton standing stocks in a mixed layer of ca 70 m. A modelling approach using 14 C observations suggested that phytoplankton growth was less than the sum of the algal loss terms within this feature. An advective supply of cells therefore would be required to sustain the observed high and constant algal biomass. In addition, although this high chlorophyll feature was initially observed during brash-ice conditions, the available data suggest that it was initiated under open water conditions.

Size-Fractionated Primary Productivity In The Northeast Atlantic In May July 1989

Size-fractionated primary productivity measurements were done in the northeast Atlantic from May to July 1989 as part of the Joint Global Ocean Flux Study (JGOFS) North Atlantic Bloom Experiment. Samples were taken on the 20°W meridian at 47, 52, 56 and 60°N, with most intensive sampling at 47 and 60°N. At the time of the first sampling at 47°N, the bloom was over but, at the other stations, substantial phytoplankton biomass and productivity were measured. The northward progression in maximum phytoplankton biomass was associated with increasing water stability and resulted in a decline in the concentration of nitrate and silicate in the surface mixed layer. The maxima in phytoplankton biomass and productivity were associated with phytoplankton cells that were larger than 5 μm diameter, but the immediate pre-bloom conditions at 60°N were dominated by small nanoplankton ( 50% of the daily productivity of 500–800 mgC m−2 day−1. In the post-bloom conditions at 47°N, nanophytoplankton again became increasingly important. Picophytoplankton (<1 μm) accounted for a constant proportion (10–15%) of the total productivity. The implications of the measured productivity of the different phytoplankton size fractions are discussed in relation to vertical flux of organic carbon and the potential transport into deep water of carbon dioxide, which has been incorporated into particulate organic matter.

Phytoplankton production and biomass estimates in the northeast Atlantic Ocean, May-June 1990

Time series measurements of size-fractionated chlorophyll a concentrations and primary production were made over the course of the spring bloom in and adjacent to a mesoscale eddy in the N.E. Atlantic as part of the U.K. Biogeochemical Ocean Flux Study 1990 Lagrangian Bloom Experiment. Substantial production, dominated by the >5μm and >1–5,μm fractions, was recorded before the main growth phase of the bloom, although total chlorophyll a concentrations varied little over this period. The main growth phase of the bloom, which occurred over approximately one week, was dominated by the > 1–5 μm fraction; a principal constituent was the small diatom Nanoneis hasleae, which almost entirely displaced larger diatoms more typical of a spring bloom population. The >5 um phytoplankton fraction became dominant for approximately two weeks following the main bloom growth phase but was replaced at the end of the observation period by the > 1–5 μm and 0.2-1 μm fractions. Phytoplankton taxonomic data for the 1990 bloom period were very different to the more typical bloom conditions of 1989. An intercomparison of14C production measurements made by U.K. and Dutch participants during the period of the Experiment using common samples gave total column productivities differing by <4%.

Luminescent whole-cell cyanobacterial bioreporter for measuring Fe availability in diverse marine environments.

ABSTRACT A Synechococcus sp. strain PCC 7002 Fe bioreporter was constructed containing the isiAB promoter fused to the Vibrio harveyi luxAB genes. Bioreporter luminescence was characterized with respect to the free ferric ion concentration in trace metal-buffered synthetic medium. The applicability of the Fe bioreporter to assess Fe availability in the natural environment was tested by using samples collected from the Baltic Sea and from the high-nutrient, low-chlorophyll subarctic Pacific Ocean. Parallel assessment of dissolved Fe and bioreporter response confirmed that direct chemical measurements of dissolved Fe should not be considered alone when assessing Fe availability to phytoplankton.

Physical, chemical and biological features of a cyclonic eddy in the region of 61°10'N 19°50'W in the North Atlantic

Abstract The second leg (CD61) of a two cruise investigation of coccolithophore biogeochemistry in the NE subarctic Atlantic provided the opportunity to make a detailed study of a cyclonic eddy in the vicinity of 61°N 20°W. The eddy field in the NE Atlantic is thought to be particularly important with regard to the physics of this region, and may influence the resulting chemical and biological properties of subarctic Atlantic waters. This eddy was ca. 50 km in diameter, moved at ca. 1.5 km d −1 to the north of east, with a geostrophic circulation around the feature of ca. 25 cm s −1 and probably extended as far as the ocean floor, where it may have interacted with the bottom topography. The horizontal salinity, nitrate and biological gradients between adjacent waters and the eddy were less marked in the present study than in a previous investigation of a cyclonic eddy in the vicinity of 48N 22°W (Mittelstaedt, 1987), possibly due to the surface waters of the eddy mixing with surrounding waters. Satellite image sequences clearly link this feature with those studied in a mesoscale coccolithophore bloom studied in the same region on a previous cruise (CD60). Rates of primary production within the eddy were almost twice the mean values reported for Ocean Weather Station India (OWSI) at this time of year, but were similar to those noted during studies at the MLML site to the SE of the eddy location. Other biological rate measurements also indicated that the NE sub-polar Atlantic in mid-summer is more active than previously thought. Despite the extensive coccolithophore bloom studied immediately previously by CD60, there was no measurable coccolithophore calcification in the waters within the eddy in the present study. This is consistent with phytoplankton taxonomic data, which demonstrates that coccolithophore abundance was almost one hundred fold lower at this location on CD61 relative to CD60 and that lith and coccolithophore abundances were grestest in the water column beneath the mixed layer, suggesting sinking. These observations suggest that the decline of the bloom had occurred in the period between the two cruises.

The Impact of Climate Change and Feedback Processes on the Ocean Carbon Cycle

We have been aware of the concept of global climate change since the advent of modern science in the 17th Century and the emergence of disciplines such as geology. However, it is only in the last century that a putative link, termed the ‘the Greenhouse Effect’ (Wood 1909), has been suggested between the atmospheric concentrations of particular gases and climate. The composition of the atmosphere has been studied routinely since the late fifties/early sixties with the establishment of monitoring sites for atmospheric CO2 (such as Mauna Loa) where the 40-year dataset clearly demonstrates the rise of atmospheric CO2 (Keeling et al. 1995). Similar anthropogenically-mediated increases in the atmos-pheric concentrations of other gases such as nitrous oxide and methane have also been recorded in the last 40 years (Bigg 1996; IPCC 2001). Such increases in the concentrations of these gases in the atmosphere alter the radiative forcing globally by decreasing the long-wave radiative flux leaving the trophosphere (Houghton et al. 1990) which is thought to lead to climatic effects. Alongside the global monitoring of atmospheric concentrations and distributions of greenhouse gases, there have been concerted efforts to use mathematical models to better understand the nature of the relationship between the observed changes in gas concentrations, subsequent alteration of radiative forcing and climate.

Micro-algal carbon and nitrogen uptake in post-coccolithophore bloom conditions in the northeast Atlantic, July 1991

Abstract A study of carbon and nitrogen uptake by phytoplankton was conducted at two sites in the subpolar northeast Atlantic during July 1991. The main study site at 61°N, 20°W was located within a cyclonic warm core eddy, and the other site was at 62°30′N, 20°W. Based on evidence of coccolithophore sedimentation and the relatively slow movement of the eddy, this structure was probably within the bounds of a mesoscale coccolithophore bloom that was in decline 10–20 days before the present study. As little is known about the conditions leading to the onset or collapse of such a bloom, the data presented here are, to our knowledge, the first to quantify phytoplankton dynamics following such an event. In addition, data from the main site provide one of the first assessments of the carbon and nitrogen dynamics within a cyclonic eddy that is typically observed in the northeast Atlantic. The findings at both sites revealed relatively high rates of primary production and concomitant uptake of inorganic nitrogen, suggesting that production rates were not enhanced within the eddy relative to the surrounding waters. These rates were comparable with those noted in late spring in the northeast Atlantic at lower latitudes (47°N, 20°W; 0.7 g C m −2 day −1 ) and are slightly in excess of modelled estimates of production for the subpolar North Atlantic in midsummer (0.5–0.6 g C m −2 day −1 ), but less than estimates based on functional photosynthetically active radiation (PAR)-productivity relationships derived from the North Atlantic Bloom Experiment (NABE) (greater than 1.0 g C m −2 day −1 ). Such functional relationships, derived at lower latitudes, may not be applicable to the subpolar northeast Atlantic. The findings of this study concur with the previous suggestion that the subpolar Atlantic is indeed productive at this time and may deserve further attention from modellers. A comparison of physical, chemical and biological conditions during the coccolithophore bloom and post-bloom periods indicates little change in environment and suggests the role of some self-regulatory mechanism, such as cell self-shading, as the cause of the collapse of the bloom. Invoking such a non-environmental factor may also explain the observed high rates of post-bloom production.

Carbon flux in ice-ocean-plankton systems of the Bellingshausen Sea during a period of ice retreat

Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature of the production system was a rapid retreat of the ice-edge, which uncoupled the marginal ice zone from a phytoplankton bloom which remained associated with a frontal system. This bloom was maintained, and probably initiated, in an unusual environment generated by the interaction between the marginal ice zone and the front. Size-based analyses of the microbial system were derived for ice-covered, recently ice-covered and open water sites. Estimates of standing stocks and key rate processes were combined to produce a single food web network for each station. The under-ice system was one of low production and low recycling but apparently high retention. As the ice retreated the microbial systems to the north began to develop, but these were constrained by grazing pressure. The bloom in the area appeared to be sustained even though estimated losses were far higher than production, although the high sedimentation losses expected were not observed. The carbon flow networks are discussed in relation to the environmental changes and the interaction of the marginal ice zone and the frontal system appears crucial to the phytoplankton. Microzooplankton grazing is implicated as a major controlling factor. The local microbial dynamics are strongly influenced by material which was produced at an earlier time and somewhere else in the Southern Ocean.

Scientific diving under sea ice in the Southern ocean

Scientific Diving techniques were employed during a 54 day oceanographic research cruise to the Bellingshausen Sea, Southern Ocean (65°S–72°S, 80°W–87°W), in order to position sampling and data collecting instrumentation beneath sea ice. Eight Scientific Divers and a Field Diving Officer safely completed 112 individual dives (range 2–80 minutes, 2–28 m); 94 of these were roped dives through holes cut in 1 m thick sea ice. Seawater temperature was −1.8°C, horizontal visibility 30 m+ and water depth 600 m or more. No problems were encountered with the diving equipment used. Diving techniques enabled the collection of an important data set describing the dynamics of phytoplankton and zooplankton growth beneath sea ice. Recommendations for future under-ice oceanic scientific diving inc1ude the use of dive tables with ascent rates of less than 15 m/min, the provision for therapeutic oxygen at the dive site, and adequate shelter for surface tenders.