Modeling estimates of the global emission of dimethylsulfide under enhanced greenhouse conditions

16 pages, 10 figures, 2 tablesWe have used a marine food-web model, an atmosphere-ocean general circulation model (GCM), and an empirical dimethylsulfide (DMS) algorithm to predict the DMS seawater concentration and the DMS sea-to-air flux in 10° latitude bands from 70°N to 70°S under contemporary and enhanced greenhouse conditions. The DMS empirical algorithm utilizes the food-web model predictions of surface chlorophyll and the GCM's simulation of oceanic mixed layer depth. The food-web model was first calibrated to contemporary climate conditions using satellite-derived chlorophyll data and meteorological forcings. For the climate change simulations, the meteorological forcings were derived from a transient simulation of the CSIRO Mark 2 GCM, using the IPCC/IS92a radiative forcing scenario to the period of equivalent CO2 tripling (2080). The globally integrated DMS flux perturbation is predicted to be + 14%; however, we found strong latitudinal variation in the perturbation. The greatest perturbation to DMS flux is simulated at high latitudes in both hemispheres, with little change predicted in the tropics and sub-tropics. The largest change in annual integrated flux (+ 106%) is simulated in the Southern Hemisphere between 50°S and 60°S. At this latitude, the DMS flux perturbation is most influenced by the GCM-simulated changes in the mixed layer depth. The results indicate that future increases in stratification in the polar oceans will play a critical role in the DMS cycle and climate change. Copyright 2004 by the American Geophysical UnionThese activities are sponsored by NASA's Mission to Planet Earth Program (http://seawifs.gsfc.nasa.gov)Peer Reviewe

Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles

Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs); six types of phytoplankton, three types of zooplankton, and heterotrophic bacteria. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing zooplankton, and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean High Nutrient Low Chlorophyll (HNLC) region during summer. When model simulations do not represent crustacean macrozooplankton grazing, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there was no iron deposition from dust. When model simulations included the developments of the zooplankton component, the simulation of phytoplankton biomass improved and the high chlorophyll summer bias in the Southern Ocean HNLC region largely disappeared. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community rather than iron limitation. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean

The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set

Background Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables. Methods Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set. Results Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001). Conclusions The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy

Spring mortality of the cyclopoid copepod Oithona similis in polar waters

The cyclopoid copepod Oithona similis is highly abundant and ubiquitous in the marine epipelagic environment, yet rates of mortality in this species have rarely been quantified; indeed we are lacking such measurements for Copepoda in general in cold waters. In the present study we examined O. similis stage structure, egg production and mortality rates across the Scotia Sea, Southern Ocean, sampling from the ice edge to the Polar Front in the austral spring of 2006, The population stage structure near the retreating ice edge was indicative of a recruitment pulse moving through the younger stages; therefore, the assumptions of the vertical life table (VLT) approach were not met and mortality was not estimated for those stations. At all other stations the assumptions of VLT were largely met, and mortality rates were determined as across-station averages, The highest rates of mortality occurred across the egg to NIT stages at around 0.04 d(-1), falling to < 0.03 d(-1) in subsequent stages, and then increasing again to 0.11. d(-1) across copepod stage V to adult males. The ratio of adult males to females suggested that males have a mortality rate similar to 12 times greater than females (i.e. the adult male to female abundance ratio is 0.08). It is unlikely that these differences can be attributed simply to the males' shorter physiological longevity (longevity when free of predators); the primary cause is likely elevated predation mortality due to the risks associated with mate locating behaviour

Fecundity of marine planktonic copepods: global rates and patterns in relation to chlorophyll a, temperature and body weight

Global rates and patterns of fecundity in marine epipelagic copepods were studied as a function of temperature, body weight of the female and concentration of chlorophyll a. We divided data into 3 groups: broadcast spawners, sac spawners (including calanoids, cyclopoids and harpacticoids) and poecilostomatoids; although the latter are sac spawners, they were treated separately, but data were too sparse to examine patterns. Fecundity was positively correlated with temperature and body weight in both broadcast and sac spawners. Michaelis-Menten relationships revealed that fecundity rates are significantly related to chlorophyll a (chl a) concentration for broadcasters, but not so for sac spawners. Broadcasting copepods have a maximum fecundity (f(max)) of 47 eggs female(-1) d(-1), with a half-saturation coefficient (K-m) of 2.4 mug chl a l(-1), for a body weight of 10 mugC individual(-1), when all data are adjusted to 15degreesC. In contrast, fecundity rates in sac spawners are ca. 5 eggs female(-1) d(-1). Of the broadcaster genera examined, Centropages spp. has the highest f(max) at 71 eggs female(-1) d(-1) (data corrected to 15degreesC), and Paracalanus spp. the lowest f(max) at 25 eggs female(-1) d(-1). In the sac-spawning Pseudocalanus spp. we found a significant relationship between fecundity and chl a, with an f(max) of only 7.8 eggs female(-1) d(-1), while for Oithona spp. no significant relationship was evident. By comparing in situ with laboratory food-saturated rates we were able to assess the degree to which fecundity is food-limited in the natural environment. The degree of food limitation increases with increasing temperature in sac spawners; at low temperatures (similar to5degreesC) in situ rates are similar to laboratory food-saturated rates, but at 25degreesC rates are 23% of laboratory food-saturation values. In nature, increasing food limitation with increasing temperature may be the result of greater food requirements to balance respiration demands, i.e. decreasing net growth efficiency in warmer situations. It may also be due to lower availability of suitable food in terms of quality or quantity with increasing temperature, possibly as a result of increased dominance of smaller phytoplankton size fractions (e.g. picoplankton) in warm waters. Food limitation in the environment may be more severe than these comparisons suggest, as laboratory food-saturated fecundity rates in broadcasters may be as low as 36% of the in situ maximum rates (fmax rates)

A synthesis of growth rates in marine epipelagic invertebrate zooplankton

We present the most extensive study to date of globally compiled and analysed weight-specific growth rates in marine epi-pelagic invertebrate metazoan zooplankton. Using specified selection criteria, we analyse growth rates from a variety of zooplanktonic taxa, including both holo- and mero-planktonic forms, from over 110 published studies. Nine principal taxonomic groups are considered, the copepods (number of individual data points (n) - 2,528); crustaceans other than copepods (n - 253); cnidarians (n = 77); ctenophores (n = 27); chaetognaths (n = 87); pteropods (n = 8);polychaetes (n = 12); thaliaceans (n = 88); and larvaceans (n = 91). The copepods are further examined by subdividing them into broadcasters or sac-spawning species, and as nauplii (N1–N6), copepodities (C1–C5) and adults (C6). For each taxonomic group relationships between growth, temperature and body weight are examined using a variety of methods. Weight-specific growth tends to increase with increasing temperature and with decreasing body weight in the crustacean group. Growth does nor relate to body weight in the case of chaetognaths and larvaceans, but does increase with temperature. In the cnidarian and ctenophore groups growth does not relate to temperature, but is negatively related to body size. For the thaliaceans growth increases with both increasing body weight and temperature. In the entire broadcasting copepod data set, weight-specific growth increases with increasing temperature and decreasing body weight. In sac-spawners, growth increase with increasing temperature, and increases with decreasing body weight at temperatures below 20°C, but decrease with body weight at temperatures above this. Comparison between the different taxa shows important differences and similarities. Our extensive synthesis of data generally confirms that larvaceans, pteropods, cnidarians and ctenophores have rates of weigth-specific growth that are typically greater than the copepods, chaetognaths and other crustaceans of similar carbon weight. For the cnidarians, ctenophores adn larvaceans groth rates are almost always greater than the general relationship describing copepod growth, and are also at the upper limits or beyond the maximum rates for copepods of a similar weight. For the pteropods, growth rates are generally greater than those of copepods, although the data set was limited to a single carnivorous species in a single study (i.e. Clione limacina). The thaliaceans have the highest growth rates for animals with body weights greater than around 1mg C ind−1, with rates of up to 2.1 d−1 for Pegea bicaudata. Whilst the larvaceans can achieve rates of 2 d−1 in warm tropical waters (28°C), and as high as > 3 d−1 for < 0.2 mg C individual−1 animals of Oikopleura diocia. These are possibly the highest rates every recorded in epi-pelagic metazoans. Reasons for the differences between taxonomic groups are discussed in relation to intrinsic and extrinsic factors and limitations. The importance of this investigation not only lies in it being the most comprehensive overview of patterns of growth to date, but because the data set highlight the gaps in measurements and current knowledge. We examine the inadequacies in the current data sets, and in the methods being used to measure growth and production. Most of the data are for animals collected from coastal and estuarine waters, and it is clear that for a fuller understanding there is an urgent need for work in the open ocean, and for investigations outside temperature regions. There is also a need to explore the role of food availability, and how food concentrations in incubations, and under food saturation, relate to those experienced in the natural environment

Errors in juvenile copepod growth rate estimates are widespread: problems with the Moult Rate method

The ‘Moult Rate’ (MR) method has been used widely to derive stage-specific growth rates in juvenile copepods. It is the most common field-based method. Unfortunately, the equation underlying the method is wrong and, consequently, large errors in juvenile growth rate estimates are widespread. The equation derives growth from the mean weight of 2 consecutive stages (i and i + 1) and the duration of stage i. The weight change and the period to which this change is attributed are, therefore, offset. We explore this potential source of error in the MR method critically. Errors arise as a result of 2 primary factors: (1) unequal durations of successive stages and (2) unequal rates of growth of successive stages. The method of deriving the mean weight (arithmetic or geometric) also has an impact and is examined. Using a steady-state assumption, a range of scenarios and the errors that arise are examined. The literature is then reviewed and the size of errors resulting from MR method application in both field and laboratory situations is estimated. Our results suggest that the MR method can lead to large errors in growth estimation in any stage, but some stages are particularly prone. Errors for the C5 stage are often large because the following stage (the adult) does not moult, and has a different rate of body weight increase. For the same reason, errors are also great where the following stage is not actively moulting (e.g. when diapausing). In these circumstances, published work has commonly greatly underestimated growth. For example, MR growth ranges from 11 to 47% of the value derived correctly for this stage, gi_corr (calculated assuming the non-moulting stage does not grow). In late stages that are followed by actively moulting stages, the MR method has commonly given values in excess of 150% of gi_corr, but underestimation also occurs, with values <90% of gi_corr. We propose new methods and equations that overcome these problems. These equations are written with and without within-stage mortality included. The equations are relatively insensitive to mortality rates within the range found in the field, but only provided that the stage duration is not determined from moult rate. Stage duration estimates obtained from measuring moulting rates of field-collected animals are very sensitive to mortality rates of the animals prior to capture, and field mortality rates are often high enough to produce dramatic over-estimation of stage duration

Assessment of Calanus finmarchicus growth and dormancy using the aminoacyl-tRNA synthetases method

We obtained growth rates of the copepod Calanus finmarchicus at different locations across the North Atlantic between May 1998 and June 2004. Animals were incubated for 2-9 days and fed either with natural food assemblages or with cultured algae. During this period, we measured both somatic weight-specific growth rates (measured as protein change) and aminoacyl-tRNA synthetases (AARS) activity. We found a highly significant relationship between AARS activity and growth in protein content (R2 = 0.55, P < 0.001). Significant AARS activity also occurred when growth was negative, the relationship predicting an AARS activity level of ≤8.33 nmPPi·mg protein -1·h-1 when somatic growth is zero. This is because AARS activity is expected even when growth is negative, owing to the continued protein turnover in the cells. The AARS method allowed for the first time the study of protein metabolism in overwintering C. finmarchicus. Our study results showed that overwintering copepods had significantly lower values of AARS activity than non-diapausing animals (t = -3.51, P < 0.002). The AARS method opens the possibility to better understand physiology dynamics of deep-water organisms (e.g. the beginning and end of diapause). © The Author 2006. Published by Oxford University Press. All rights reserved.This work was supported by grants from the University of Las Palmas de Gran Canaria (Spain) and the Spanish Ministry of Education, Culture and Sport (MECD, EX-2002-0456) that allowed L. Y. to visit the Marine Biology Station in Espeland (Norway) and the Institute Maurice LaMontagne in Mont-Joli (Canada). [...] Completion of this work was funded by the European Social Fund (I3P programme, CSIC). This work is a contribution to the PML Core Strategic Research Programme and to the Marine Productivity UKGLOBEC Programme (NERC, NE/C508418/1)Peer Reviewe