Seasonal Patterns Of Primary Production Research Articles

A first assessment of particle flux over the South Brazil Bight continental slope

The vertical export of particulate organic carbon (POC) is a key component of the oceanic biological pump, which regulates the distribution of elements associated with primary production in the upper euphotic zone. To better understand how oceanic biogeochemical processes will respond in climate change scenarios, it is necessary to comprehend the mechanisms that regulate the magnitude and variations of POC flux among distinct oceanic domains, including the boundaries between continental margins and oceanic basins. This work is a first assessment of particle flux over the South Brazil Bight continental slope, a tropical western boundary system dominated by the Brazil Current. Total mass flux, and specific carbon, nitrogen and biogenic silica fluxes were measured periodically by two sediment traps installed at 450 m deep over the 900 m isobath, and at 750 m deep over the 2000 m isobath, from November 2016 to September 2017. Due to strong contribution of advected particles, high and extremely irregular fluxes were registered at the 900 m isobath site (mean = 1.1 g m-2 d− 1, stand. dev. ± 2.9 g m-2 d-1). The captured material suggests this sediment trap was affected by turbidity flows, which precludes the estimation of the biological pump contribution over this isobath. Over the 2000 m isobath, POC flux (3.7 mg m-2 d-1; ±2.5 mg m-2 d− 1) followed the seasonal pattern of primary production measured by satellite. POC flux was strongly correlated with biogenic silica content (r = 0.79; p < 0.01). This ballast mineral was more efficient than CaCO3 in transferring carbon from the base of the euphotic zone to 750 m. We suggest intra-seasonal variations found in the POC flux over the 2000 m isobath to be related to Brazil Current instabilities. Measurements of δ15N suggest that higher POC flux occurred during subsurface nitrate-based production regimes. A regional exponential export model is proposed, with a mean exponent (b value) of 1.4 (±0.3). Although initial, the results of this work allow us to estimate that 2.2 × 1012 g C is exported annually over the South Brazil Bight continental slope.

Striking seasonal pattern of primary production in the river-dominated ocean margin of the northern South China Sea (NSCS-RiOMar) revealed by new field and remotely sensed data

Seasonal patterns of phytoplankton biomass and primary production (PP) are important features characterizing a marine ecosystem. The South China Sea (SCS) has been arbitrarily illustrated as an ecosystem with low PP in summer and high PP in winter. However, there is an emerging consensus about a lack of unity of PP seasonality in the SCS even in the northern SCS shelf-sea. Through analysis of the distributions of the remotely sensed colored dissolved organic matter absorption coefficient, a river-dominated ocean margin in the northern SCS (NSCS-RiOMar) with the 50 m isobath as its southeastern boundary has been defined. The difference in PP seasonality between the NSCS-RiOMar and the whole shelf-sea was evaluated by both the measured and the remotely sensed depth-integrated primary production (ΣPP). A diagnostic analysis found that euphotic depth and a function of the half-saturation light intensity accounted for the seasonal variation of ΣPP in the NSCS-RiOMar. Accordingly, the Platt and Sathyendranath (1993) model plus the nearest neighbor method and the semi-analytical estimates of euphotic depth were used to compute the remotely sensed ΣPP. The average ΣPP in the NSCS-RiOMar were 1146.4, 1604.7, 979.5, and 891.3 mg C m−2 d−1 in spring, summer, autumn, and winter, respectively, contrasted with small seasonal variations in the whole shelf-sea. The unimodal ΣPP peak was in June-July in accordance with the peak of Pearl River discharge. This result was striking because previous remote sensing studies all showed the reversed seasonal pattern of ΣPP in both the NSCS-RiOMar and the whole shelf-sea. The annual PP was estimated to be 33.5 ± 2.3 Mt C yr−1 and 56.2 ± 3.2 Mt C yr−1 in the NSCS-RiOMar and the whole shelf-sea, respectively. The nutrients inputted by the China Coastal Current might account for 4–23% of ΣPP in the NSCS-RiOMar between December and February.

Assessment of the Skill of Coupled Physical–Biogeochemical Models in the NW Mediterranean

Numerical modelling is a key tool to complement the current physical and biogeochemical observational datasets. It is essential for understanding the role of oceanographic processes on marine food webs and producing climate change projections of variables affecting key ecosystem functions. In this work we evaluate the horizontal and vertical patterns of four state-of-the-art coupled physical-biogeochemical models, three of them already published. Two of the models include data assimilation, physical and/or biological, and two do not. Simulations are compared to the most exhaustive dataset of in situ observations in the North Western Mediterranean, built ad hoc for this work, comprising gliders, conventional CTD surveys and complemented with satellite observations. The analyses are performed both in the whole domain and in four sub-regions (Catalan Shelf, Ebro Delta, Mallorca Channel and Ibiza Channel), characterized by a priori divergent primary production dynamics and driving mechanisms. Overall, existing models offer a reasonable representation of physical processes including stratification, surface temperature and surface currents, but it is shown that relatively small differences among them can lead to large differences in the response of biogeochemical variables. Our results show that all models are able to reproduce the main seasonal patterns of primary production both at the upper layer and at the Deep Chlorophyll Maximum (DCM), as well as the differential behaviour of the four sub-regions. However, there are significant discrepancies in the local variability of the intensity of the winter mixing, phytoplankton blooms or the intensity and depth of the DCM. All model runs show markedly contrasting patterns of interannual phytoplankton biomass in all four sub-regions. This lack of robustness should dissuade end-users from using them to fill gaps in time series observations without assessing their appropriateness. Finally, we discuss the usability of these models for different applications in marine ecology, including fisheries oceanography.

Primary productivity in the Gulf of Riga (Baltic Sea) in relation to phytoplankton species and nutrient variability

Summary The seasonal patterns of primary production, phytoplankton biomass, chlorophyll a, and nutrients were investigated in the central part of the Gulf of Riga (Baltic Sea) during 2011 and 2012. Annual primary productivity in the gulf was in the range of 353.4–376.2 gC m−2. Maximum carbon fixation rates occurred during the phytoplankton spring bloom from April to May when the winter nutrient pool was rapidly exhausted, suggesting the use of regenerated nutrients already in spring. The new production calculated on the draw-down of nitrates amounted to 51.80% of spring net community production. The production rates during summer were considerably lower owing to the availability of only regenerated nutrients and limited nitrogen fixation. Autumn was established as the least productive season. In autumn despite the elevated nutrient concentrations, the increasingly limited light hindered photosynthetic activity. Species governing the nutrient fluxes and the productivity of the Gulf of Riga are the diatom species responsible for new production in spring. The photosynthetic ciliate Mesodinium rubrum ((Lohmann) Hamburger & Buddenbrock 1911) prevailed in all seasons and significantly correlated with elevated productivity, while diazotrophic cyanobacteria Aphanizomenon flosaquae (Ralfs ex Bornet & Flahault 1886) contributed to new production in the summer nutrient regenerating system.

How Well Does Chlorophyll Explain the Seasonal Variation in Phytoplankton Activity?

The seasonal variation in phytoplankton activity is determined by analysing 1385 primary production (PP) profiles, chlorophyll a (Chl) concentration profiles and phytoplankton carbon biomass concentrations (C) from the period 1998–2012. The data was collected at six different stations in the Baltic Sea transition zone (BSTZ) which is a location with strong seasonal production patterns with light as the key parameter controlling this productivity. We show that the use of Chl as a proxy for phytoplankton activity strongly overestimates the contribution from the spring production to annual pelagic carbon flow. Spring (February and March) Chl comprised 16–30% of the total annual Chl produced, whereas spring C was much lower (8–23%) compared to the annual C. Spring PP accounted for 10–18% of the total annual PP, while the July–August production contributed 26–33%, i.e. within the time frame when zooplankton biomass and grazing pressure are highest. That is, Chl failed in this study to reflect the importance of the high summer PP. A better proxy for biomass may be C, which correlated well with the seasonal pattern of PP (Pearson correlation, p < 0.05). Thus, this study suggests to account for the strong seasonal pattern in C/Chl ratios when considering carbon flow in coastal systems. Seasonal data for PP were fitted to a simple sinusoidal wave model describing the seasonal distribution of PP in the BSTZ and were proposed to present a better parameterizaton of PP in shallow stratified temperate regions than more commonly applied proxies.

Spring seasonal pattern of primary production in the Gulf of Riga (Baltic Sea) after a mild winter

Spring seasonal pattern of primary production in the Gulf of Riga (Baltic Sea) after a mild winter

Benthic Oxygen Uptake in the Arctic Ocean Margins - A Case Study at the Deep-Sea Observatory HAUSGARTEN (Fram Strait).

The past decades have seen remarkable changes in the Arctic, a hotspot for climate change. Nevertheless, impacts of such changes on the biogeochemical cycles and Arctic marine ecosystems are still largely unknown. During cruises to the deep-sea observatory HAUSGARTEN in July 2007 and 2008, we investigated the biogeochemical recycling of organic matter in Arctic margin sediments by performing shipboard measurements of oxygen profiles, bacterial activities and biogenic sediment compounds (pigment, protein, organic carbon, and phospholipid contents). Additional in situ oxygen profiles were performed at two sites. This study aims at characterizing benthic mineralization activity along local bathymetric and latitudinal transects. The spatial coverage of this study is unique since it focuses on the transition from shelf to Deep Ocean, and from close to the ice edge to more open waters. Biogeochemical recycling across the continental margin showed a classical bathymetric pattern with overall low fluxes except for the deepest station located in the Molloy Hole (5500 m), a seafloor depression acting as an organic matter depot center. A gradient in benthic mineralization rates arises along the latitudinal transect with clearly higher values at the southern stations (average diffusive oxygen uptake of 0.49 ± 0.18 mmol O2 m-2 d-1) compared to the northern sites (0.22 ± 0.09 mmol O2 m-2 d-1). The benthic mineralization activity at the HAUSGARTEN observatory thus increases southward and appears to reflect the amount of organic matter reaching the seafloor rather than its lability. Although organic matter content and potential bacterial activity clearly follow this gradient, sediment pigments and phospholipids exhibit no increase with latitude whereas satellite images of surface ocean chlorophyll a indicate local seasonal patterns of primary production. Our results suggest that predicted increases in primary production in the Arctic Ocean could induce a larger export of more refractory organic matter due to the longer production season and the extension of the ice-free zone.

The annual patterns of photosynthesis in two large, freshwater, ultra-oligotrophic Antarctic lakes

The phytoplankton productivity and biomass of two large, freshwater Antarctic lakes (Vestfold Hills, eastern Antarctica) were investigated over a 12-month period. Crooked Lake was sampled at one site, while Lake Druzhby, a complex lake with two shallow and one deep basin, was subject to a more detailed investigation. Concentrations of chlorophyll a were usually below 1 µg l–1, indicating ultra-oligotrophic conditions. Despite periodic low nutrient levels, low temperatures (range 0.4–2.8°C) and periodic poor light climate, some degree of photosynthesis was measurable throughout the year, including the dark winter phase. Snow cover had a pronounced impact on the light climate of the water column and inhibited photosynthesis. Mean rates of carbon fixation in the 0- to 15-m water column varied between 0 and 38.47 µg C l–1 day–1 in Crooked Lake and 0.24 and 37.68 µg C l–1 day–1 in Lake Druzhby. There were significant differences in the seasonal patterns of primary production between the basins of Lake Druzhby. The shallow basins had highest productivity in August, whereas the deep basin had highest rates in summer. Chlorophyll specific rates of photosynthesis or assimilation numbers [µg C (chl. a)–1 h–1] varied between 0.05 and 44.9, and photosynthetic efficiency [µg C (chl. a)–1 h–1 µmol m–2 s–1] between 0.02 and 5.19. The data suggest that the phytoplankton of these lakes is adapted to low irradiance levels, low temperatures and nutrient limitation.

Lipid biogeochemistry in the Laurentian Trough: I—fatty acids, sterols and aliphatic hydrocarbons in rapidly settling particles

Sinking particles intercepted at 150 m depth in May and July at landward (L) and seaward (S) sites in the Laurentian Trough contained 540–2910 μg g −1 of fatty acids (FA), 54–990 μg g −1 of sterols and 101–184 μg g −1 of aliphatic hydrocarbons. The vertical fluxes averaged 7.2, 3.1 and 0.8 mg m −2 d −1, respectively. FA fluxes (greater at site L) and concentrations (higher at S and during July) reflected the terrestrial-marine gradient and the seasonal patterns of primary production in the estuary. Unresolved anthropogenic hydrocarbons (UCM) displayed an opposite trend. The sources and behaviour of individual lipid biomarkers were evaluated by multivariate techniques. FA 16:0 and 16:1, heneicosahexaene and 24-methylcholest-5-en-3β-ol were the most consistent tracers of an early diatom bloom sampled at the seaward site. FA 14:0 and 15:0, squalene and 24-methylcholesta-5,22E-dien-3β-ol also traced this event but were less specific. The summer increase of primary production was reflected by cholestanol, 24-methylenecholesterol, 24-norcholesta-5,22E-dien-3β-ol, 24-ethylcholesta-5,22E-dien-3β-ol and dinosterol. Zooplanktonic pristane, unsaturated FA, cholesterol and cholesta-5,22E-dien-3β-ol, were abundant in all the traps. At the landward site, cholesterol and cholesta-5,22E-dien-3β-ol covaried with dinosterol, suggesting a dinoflagellate contribution as well. These samples were very heterogeneous and showed variable inputs from higher plants (stigmastanol, FA 24:0, 26:0, long-chain n-alkanes), petrogenic hydrocarbons ( n-alkanes, UCM) and plankton (unsaturated FA, cholesterol), reflecting the combined contribution from the Upper St. Lawrence Estuary, Saguenay Fjord and a periodic upwelling.

Biogeochemistry of organic matter in the Laurentian Trough, I. Composition and vertical fluxes of rapidly settling particles

Abstract Settling particles from duplicate free-drifting sediment traps were collected at 150 m depth in May and July at a landward and a seaward site in the 350 m deep Laurentian Trough. The total organic carbon (TOC) fluxes were high (95–454 mg/m2/d), comparable to those reported for Dabob Bay (a similar moderately productive deep coastal environment) and for the highly productive Peru upwelling region. The TOC (26–67 mg C g ) consisted of lipids (17–37%), carbohydrates (7.9–16%), hydrolysable amino acids (8.4–16%), labile proteins (0.3–2.6%), and a non-characterized fraction (40–64%). Amino acids, proteins and uncharacterized compounds accounted for 24–42, 1–10 and 58–76%, respectively, of total nitrogen (2.3–7.7 mg N/g). The pigment fraction was largely dominated by pheopigments (0.06-1.15 mg/g vs 0.004–0.15 mg/g for chlorophyll a). C N and C pigment ratios indicated that on average, about half of the carbon flux was of terrigenous origin. Marine sources included a dominant zooplanktonic contribution, indicated by the abundance of fecal pellets, lipids and pheopigments, and a smaller contribution from fresh algae. Cluster and correlation analyses confirmed the decoupling of pigment and TOC fluxes and the strong zooplanktonic influence of the trap material. Despite large day-to-day and inter-trap variability, clear differences were observed in the fluxes, TOC content and composition at both sampling sites and months. Such trends are attributed to the relative contribution from terrestrial and marine sources and seasonal patterns of primary production.

Seasonal Patterns of Planktonic Production in McMurdo Sound, Antarctica

The prolonged periods of continuous darkness and light in polar regions have resulted in a unique seasonal partitioning of primary and heterotrophic production. In McMurdo Sound for example, the biomass, size distribution and production by phytoplankton and bacterioplankton undergo distinct seasonal cycles. The seasonal pattern of primary production appeared to be regulated by light whereas the three order of magnitude change in phytoplankton biomass during mid- to late December was largely controlled by the advection of planktonic algae from the Ross Sea into McMurdo Sound. The size distribution of phytoplankton was highly seasonal; nano- and picoplankton were dominant from August through November while netplankton were more abundant in December and January. Seasonal variations of bacterial biomass and production were smaller than those of phytoplankton. During the late austral winter and spring, bacterial biomass and production exceeded those of phytoplankton. This implies that during this period, organic material from allochthonous sources sustained bacterial growth. During the late spring and summer, however, the pattern was reversed and autochthonous primary production was sufficient to support concurrent bacterioplankton production. The apparent temporal disequilibrium in autochthonous bacterioplankton and phytoplankton production was maintained by the seasonal input of allochthonous organic material into McMurdo Sound. The facts that a) bacteria were both abundant and highly active, b) bacterivory was common among many of the endemic protozoa and some planktonic metazoa and c) these bacterivores consumed >95% of the bacterial production strongly suggest that bacteria are a crucial component in the transfer of energy and material to metazoans in polar regions.

Seasonality in the antarctic marine environment

1. 1. The Southern Ocean is characterized by the combination of a low but stable temperature with a markedly seasonal pattern of primary production. It therefore offers an environment where the annual variations in temperature and production are uncoupled and it is possible to distinguish the effects of one from the other. 2. 2. The widely observed slow growth of polar marine ectotherms is not due to a direct limitation by the low temperature. Rather the seasonal pattern of growth in many species, together with the frequent limitation of reproduction to the summer months, indicate that many processes are regulated strictly by the availability of food (that is they are resource limited). 3. 3. The degree of seasonality in the biology of polar marine organisms varies with their position in the food web. In general, herbivores have highly seasonal life-histories, whereas carnivores, scavengers and higher level predators show less seasonal patterns of growth or reproduction.