Thomas R. Anderson

Bio: Thomas R. Anderson is an academic researcher from National Oceanography Centre. The author has contributed to research in topics: Phytoplankton & Dissolved organic carbon. The author has an hindex of 43, co-authored 100 publications receiving 6419 citations. Previous affiliations of Thomas R. Anderson include University of Southampton & Natural Environment Research Council.

Carbon sequestration in ecosystems: the role of stoichiometry

Abstract: The fate of carbon (C) in organisms, food webs, and ecosystems is to a major extent regulated by mass-balance principles and the availability of other key nutrient elements. In relative terms, nutrient limitation implies excess C, yet the fate of this C may be quite different in autotrophs and heterotrophs. For autotrophs nutrient limitation means less fixation of inorganic C or excretion of organic C, while for heterotrophs nutrient limitation means that more of ingested C will “go to waste” in the form of egestion or respiration. There is in general a mismatch between autotrophs and decomposers that have flexible but generally high C:element ratios, and consumers that have lower C:element ratios and tighter stoichiometric regulation. Thus, C-use efficiency in food webs may be governed by the element ratios in autotroph biomass and tend to increase when C:element ratios in food approach those of consumers. This tendency has a strong bearing on the sequestration of C in ecosystems, since more C will be di...

HORIZONS Plankton functional type modelling: running before we can walk?

Abstract: Biogeochemical cycling in marine systems is intimately linked to the activity of specific plankton functional types (PFTs) such as diatoms, coccolithophores and nitrogen fixers, thereby providing a focus for contemporary modelling studies. Incorporating extra complexity beyond simple nutrientphytoplankton-zooplankton-detritus (NPZD) models is, however, fraught with difficulties: poorly understood ecology; lack of data; aggregating diversity within functional groups into meaningful state variables and constants; sensitivity of output to the parameterizations in question and their physical and chemical environment. Although regional models addressing the seasonal succession of plankton types have achieved some degree of success, predicted distributions of PFTs in global biogeochemical models have thus far been less than convincing. While the continued articulation of detail in ecosystem models is surely the way forward, I argue that this can only be so with due care and attention to the formulations employed and a healthy dose of scepticism regarding model outcomes. Future directions should emphasize building up complexity gradually, objective assessment of the resulting parameterizations, and variety in approach such as the use of empirical alternatives to the fully dynamic representation of PFTs in models.

Plankton functional type modelling : running before we can walk?

Abstract: Biogeochemical cycling in marine systems is intimately linked to the activity of specific plankton functional types (PFTs) such as diatoms, coccolithophores and nitrogen fixers, thereby providing a focus for contemporary modelling studies. Incorporating extra complexity beyond simple nutrient-phytoplankton-zooplankton-detritus (NPZD) models is, however, fraught with difficulties: poorly understood ecology; lack of data; aggregating diversity within functional groups into meaningful state variables and constants; sensitivity of output to the parameterizations in question and their physical and chemical environment. Although regional models addressing the seasonal succession of plankton types have achieved some degree of success, predicted distributions of PFTs in global biogeochemical models have thus far been less than convincing. While the continued articulation of detail in ecosystem models is surely the way forward, I argue that this can only be so with due care and attention to the formulations employed and a healthy dose of scepticism regarding model outcomes. Future directions should emphasize building up complexity gradually, objective assessment of the resulting parameterizations, and variety in approach such as the use of empirical alternatives to the fully dynamic representation of PFTs in models.

Reconciliation of the carbon budget in the ocean’s twilight zone

Abstract: Photosynthesis in the surface ocean produces approximately 100 gigatonnes of organic carbon per year, of which 5 to 15 per cent is exported to the deep ocean. The rate at which the sinking carbon is converted into carbon dioxide by heterotrophic organisms at depth is important in controlling oceanic carbon storage. It remains uncertain, however, to what extent surface ocean carbon supply meets the demand of water-column biota; the discrepancy between known carbon sources and sinks is as much as two orders of magnitude. Here we present field measurements, respiration rate estimates and a steady-state model that allow us to balance carbon sources and sinks to within observational uncertainties at the Porcupine Abyssal Plain site in the eastern North Atlantic Ocean. We find that prokaryotes are responsible for 70 to 92 per cent of the estimated remineralization in the twilight zone (depths of 50 to 1,000 metres) despite the fact that much of the organic carbon is exported in the form of large, fast-sinking particles accessible to larger zooplankton. We suggest that this occurs because zooplankton fragment and ingest half of the fast-sinking particles, of which more than 30 per cent may be released as suspended and slowly sinking matter, stimulating the deep-ocean microbial loop. The synergy between microbes and zooplankton in the twilight zone is important to our understanding of the processes controlling the oceanic carbon sink.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Carbon and Other Biogeochemical Cycles

Abstract: For base year 2010, anthropogenic activities created ~210 (190 to 230) TgN of reactive nitrogen Nr from N2. This human-caused creation of reactive nitrogen in 2010 is at least 2 times larger than the rate of natural terrestrial creation of ~58 TgN (50 to 100 TgN yr−1) (Table 6.9, Section 1a). Note that the estimate of natural terrestrial biological fixation (58 TgN yr−1) is lower than former estimates (100 TgN yr−1, Galloway et al., 2004), but the ranges overlap, 50 to 100 TgN yr−1 vs. 90 to 120 TgN yr−1, respectively). Of this created reactive nitrogen, NOx and NH3 emissions from anthropogenic sources are about fourfold greater than natural emissions (Table 6.9, Section 1b). A greater portion of the NH3 emissions is deposited to the continents rather than to the oceans, relative to the deposition of NOy, due to the longer atmospheric residence time of the latter. These deposition estimates are lower limits, as they do not include organic nitrogen species. New model and measurement information (Kanakidou et al., 2012) suggests that incomplete inclusion of emissions and atmospheric chemistry of reduced and oxidized organic nitrogen components in current models may lead to systematic underestimates of total global reactive nitrogen deposition by up to 35% (Table 6.9, Section 1c). Discharge of reactive nitrogen to the coastal oceans is ~45 TgN yr−1 (Table 6.9, Section 1d). Denitrification converts Nr back to atmospheric N2. The current estimate for the production of atmospheric N2 is 110 TgN yr−1 (Bouwman et al., 2013).

The Ecology of Phytoplankton

Abstract: Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

Bacterial growth efficiency in natural aquatic systems

Abstract: Heterotrophic bacteria perform two major functions in the transformation of organic matter: They produce new bacterial biomass (bacterial secondary production [BP]), and they respire organic C to inorganic C (bacterial respiration [BR]). For planktonic bacteria, a great deal has been learned about BP and its regulation during the past several decades but far less has been learned about BR. Our lack of knowledge about BR limits our ability to understand the role of bacteria in the carbon cycle of aquatic ecosystems. Bacterial growth efficiency (BGE) is the amount of new bacterial biomass produced per unit of organic C substrate assimilated and is a way to relate BP and BR: BGED (BP)=(BPC BR). Estimates of BGE for natural planktonic bacteria range from <0.05 to as high as 0.6, but little is known about what might regulate this enormous range. In this paper we review the physiological and ecological bases of the regulation of BGE. Further, we assemble the literature of the past 30 years for which both BP and BR were measured in natural planktonic ecosystems and explore the relationship between BGE and BP. Although the relationship is variable, BGE varies systematically with BP and the trophic richness of the ecosystem. In the most dilute, oligotrophic systems, BGE is as low as 0.01; in the most eutrophic systems, it plateaus near 0.5. Planktonic bacteria appear to maximize carbon utilization rather than BGE. A consequence of this strategy is that maintenance energy costs (and therefore maintenance respiration) seems to be highest in oligotrophic systems.