Law Cliff S.
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PreprintThe SOLAS air-sea gas exchange experiment (SAGE) 2004( 2010-03-11) Harvey, Mike J. ; Law, Cliff S. ; Smith, Murray J. ; Hall, Julie A. ; Abraham, Edward R. ; Stevens, Craig L. ; Hadfield, Mark G. ; Ho, David T. ; Ward, Brian ; Archer, Stephen D. ; Cainey, Jill M. ; Currie, Kim I. ; Devries, Dawn ; Ellwood, Michael J. ; Hill, Peter ; Jones, Graham B. ; Katz, Dave ; Kuparinen, Jorma ; Macaskill, Burns ; Main, William ; Marriner, Andrew ; McGregor, John ; McNeil, Craig L. ; Minnett, Peter J. ; Nodder, Scott D. ; Peloquin, Jill ; Pickmere, Stuart ; Pinkerton, Matthew H. ; Safi, Karl A. ; Thompson, Rona ; Walkington, Matthew ; Wright, Simon W. ; Ziolkowski, Lori A.The SOLAS air-sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive Subpolar Zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a Lagrangian study quantifying key biological and physical drivers influencing the air-sea gas exchange processes of CO2, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF6/3He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air-sea tracer exchange at the 10’s of km’s scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describes air-sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties, and wind speed were quantified to further assist the development of gas exchange models for high-wind environments. There was a significant increase in the photosynthetic competence (Fv/Fm) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary production and column-integrated chlorophyll a concentrations had only doubled relative to the unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions totalling 1.1 tonne Fe2+, this was a very modest response compared to the other mesoscale iron enrichment experiments. An investigation of the factors limiting bloom development considered co- limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst incident light levels and the initial Si:N ratio were the lowest recorded in all FeAX’s to date, there was only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing were all considered as factors that prevented significant biomass accumulation. In line with the limited response, the enhanced biological draw-down of pCO2 was small and masked by a general increase in pCO2 due to mixing with higher pCO2 waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX’s dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX’s. In the context of iron fertilisation as a geoengineering tool for atmospheric CO2 removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition.
ArticleSynthesis of iron fertilization experiments : from the Iron Age in the Age of Enlightenment(American Geophysical Union, 2005-09-28) Baar, Hein J. W. de ; Boyd, Philip W. ; Coale, Kenneth H. ; Landry, Michael R. ; Tsuda, Atsushi ; Assmy, Philipp ; Bakker, Dorothee C. E. ; Bozec, Yann ; Barber, Richard T. ; Brzezinski, Mark A. ; Buesseler, Ken O. ; Boye, Marie ; Croot, Peter L. ; Gervais, Frank ; Gorbunov, Maxim Y. ; Harrison, Paul J. ; Hiscock, William T. ; Laan, Patrick ; Lancelot, Christiane ; Law, Cliff S. ; Levasseur, Maurice ; Marchetti, Adrian ; Millero, Frank J. ; Nishioka, Jun ; Nojiri, Yukihiro ; van Oijen, Tim ; Riebesell, Ulf ; Rijkenberg, Micha J. A. ; Saito, Hiroaki ; Takeda, Shigenobu ; Timmermans, Klaas R. ; Veldhuis, Marcel J. W. ; Waite, Anya M. ; Wong, Chi-ShingComparison of eight iron experiments shows that maximum Chl a, the maximum DIC removal, and the overall DIC/Fe efficiency all scale inversely with depth of the wind mixed layer (WML) defining the light environment. Moreover, lateral patch dilution, sea surface irradiance, temperature, and grazing play additional roles. The Southern Ocean experiments were most influenced by very deep WMLs. In contrast, light conditions were most favorable during SEEDS and SERIES as well as during IronEx-2. The two extreme experiments, EisenEx and SEEDS, can be linked via EisenEx bottle incubations with shallower simulated WML depth. Large diatoms always benefit the most from Fe addition, where a remarkably small group of thriving diatom species is dominated by universal response of Pseudo-nitzschia spp. Significant response of these moderate (10–30 μm), medium (30–60 μm), and large (>60 μm) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of “dissolved” Fe (filtrate < 0.2 μm) maintained during an experiment determines the dominant diatom size class. However, this is further complicated by continuous transfer of original truly dissolved reduced Fe(II) into the colloidal pool, which may constitute some 75% of the “dissolved” pool. Depth integration of carbon inventory changes partly compensates the adverse effects of a deep WML due to its greater integration depths, decreasing the differences in responses between the eight experiments. About half of depth-integrated overall primary productivity is reflected in a decrease of DIC. The overall C/Fe efficiency of DIC uptake is DIC/Fe ∼ 5600 for all eight experiments. The increase of particulate organic carbon is about a quarter of the primary production, suggesting food web losses for the other three quarters. Replenishment of DIC by air/sea exchange tends to be a minor few percent of primary CO2 fixation but will continue well after observations have stopped. Export of carbon into deeper waters is difficult to assess and is until now firmly proven and quite modest in only two experiments.
ArticleA Climate Change Atlas for the Ocean(Oceanography Society, 2011-06) Boyd, Philip W. ; Law, Cliff S. ; Doney, Scott C.At both regional and national levels, there is an urgent need to develop a clear picture of how climate change will alter multiple environmental properties in the ocean. Specifically, what will such cumulative alterations mean for local biological productivity, ecosystem services, climate feedbacks, and related effects ranging from biodiversity to economics? Currently, a wide range of confounding issues, such as the plethora and complexity of information in the public domain, hinders accommodating climate change into future planning and development of ocean resource management strategies. This impediment is especially true at the regional level, for example, within national Exclusive Economic Zones (EEZs), where critical management decisions are made but for which substantial uncertainty clouds climate change projections and ecosystem impact assessments. Evaluating the susceptibility of a nation's marine resources to climate change requires knowledge of the geographic and seasonal variations in environmental properties over an EEZ and the range, spatial patterns, and uncertainty of projected climate change in those properties (Boyd et al., 2007). Furthermore, information is needed on the climate sensitivity of the biological species or strains that comprise particular marine resources (Boyd et al., 2007; Nye et al., 2009) and/or contribute to food-web interactions, and also on potential implications for human resource exploitation patterns and intensity.
ArticleAn intercomparison of oceanic methane and nitrous oxide measurements(Copernicus Publications on behalf of the European Geosciences Union, 2018-10-05) Wilson, Samuel T. ; Bange, Hermann W. ; Arévalo-Martínez, Damian L. ; Barnes, Jonathan ; Borges, Alberto V. ; Brown, Ian ; Bullister, John L. ; Burgos, Macarena ; Capelle, David W. ; Casso, Michael A. ; de la Paz, Mercedes ; Farías, Laura ; Fenwick, Lindsay ; Ferrón, Sara ; Garcia, Gerardo ; Glockzin, Michael ; Karl, David M. ; Kock, Annette ; Laperriere, Sarah ; Law, Cliff S. ; Manning, Cara C. ; Marriner, Andrew ; Myllykangas, Jukka-Pekka ; Pohlman, John W. ; Rees, Andrew P. ; Santoro, Alyson E. ; Tortell, Philippe D. ; Upstill-Goddard, Robert C. ; Wisegarver, David P. ; Zhang, Gui-Ling ; Rehder, GregorLarge-scale climatic forcing is impacting oceanic biogeochemical cycles and is expected to influence the water-column distribution of trace gases, including methane and nitrous oxide. Our ability as a scientific community to evaluate changes in the water-column inventories of methane and nitrous oxide depends largely on our capacity to obtain robust and accurate concentration measurements that can be validated across different laboratory groups. This study represents the first formal international intercomparison of oceanic methane and nitrous oxide measurements whereby participating laboratories received batches of seawater samples from the subtropical Pacific Ocean and the Baltic Sea. Additionally, compressed gas standards from the same calibration scale were distributed to the majority of participating laboratories to improve the analytical accuracy of the gas measurements. The computations used by each laboratory to derive the dissolved gas concentrations were also evaluated for inconsistencies (e.g., pressure and temperature corrections, solubility constants). The results from the intercomparison and intercalibration provided invaluable insights into methane and nitrous oxide measurements. It was observed that analyses of seawater samples with the lowest concentrations of methane and nitrous oxide had the lowest precisions. In comparison, while the analytical precision for samples with the highest concentrations of trace gases was better, the variability between the different laboratories was higher: 36% for methane and 27% for nitrous oxide. In addition, the comparison of different batches of seawater samples with methane and nitrous oxide concentrations that ranged over an order of magnitude revealed the ramifications of different calibration procedures for each trace gas. Finally, this study builds upon the intercomparison results to develop recommendations for improving oceanic methane and nitrous oxide measurements, with the aim of precluding future analytical discrepancies between laboratories.