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Net Primary Production in the Ocean

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Abstract

Net Primary Production (NPP) is the rate of photosynthetic carbon fixation minus the fraction of fixed carbon used for cellular respiration and maintenance by autotrophic planktonic microbes and benthic plants (Sections 6.2.1, 6.3.1). Environmental drivers of NPP include light, nutrients, micronutrients, CO 2 , and temperature (Figure PP-1a). These drivers, in turn, are influenced by oceanic and atmospheric processes, including cloud cover; sea ice extent; mixing by winds, waves, and currents; convection; density stratification; and various forms of upwelling induced by eddies, frontal activity, and boundary currents. Temperature has multiple roles as it influences rates of phytoplankton physiology and heterotrophic bacterial recycling of nutrients, in addition to stratification of the water column and sea ice extent (Figure PP-1a). Climate change is projected to strongly impact NPP through a multitude of ways that depend on the regional and local physical settings (WGI AR5, Chapter 3), and on ecosystem structure and functioning (medium confidence; Sections 6.3.4, 6.5.1). The influence of environmental drivers on NPP causes as much as a 10-fold variation in regional productivity with nutrient-poor subtropical waters and light-limited Arctic waters at the lower range and productive upwelling regions and highly eutrophic coastal regions at the upper range (Figure PP-1b).
Net Primary Production in
the Ocean
Philip W. Boyd (New Zealand), Svein Sundby (Norway), Hans-Otto Pörtner (Germany)
PP
133
Net Primary Production (NPP) is the rate of photosynthetic carbon fixation minus the fraction of
fixed carbon used for cellular respiration and maintenance by autotrophic planktonic microbes
and benthic plants (Sections 6.2.1, 6.3.1). Environmental drivers of NPP include light, nutrients,
micronutrients, CO2, and temperature (Figure PP-1a). These drivers, in turn, are influenced by
oceanic and atmospheric processes, including cloud cover; sea ice extent; mixing by winds, waves,
and currents; convection; density stratification; and various forms of upwelling induced by eddies,
frontal activity, and boundary currents. Temperature has multiple roles as it influences rates
of phytoplankton physiology and heterotrophic bacterial recycling of nutrients, in addition to
stratification of the water column and sea ice extent (Figure PP-1a). Climate change is projected
to strongly impact NPP through a multitude of ways that depend on the regional and local
physical settings (WGI AR5, Chapter 3), and on ecosystem structure and functioning (medium
confidence; Sections 6.3.4, 6.5.1). The influence of environmental drivers on NPP causes as much
as a 10-fold variation in regional productivity with nutrient-poor subtropical waters and light-
limited Arctic waters at the lower range and productive upwelling regions and highly eutrophic
coastal regions at the upper range (Figure PP-1b).
The oceans currently provide ~50 × 1015 g C yr–1, or about half of global NPP (Field et al., 1998).
Global estimates of NPP are obtained mainly from satellite remote sensing (Section 6.1.2),
which provides unprecedented spatial and temporal coverage, and may be validated regionally
against oceanic measurements. Observations reveal significant changes in rates of NPP when
environmental controls are altered by episodic natural perturbations, such as volcanic eruptions
enhancing iron supply, as observed in high-nitrate low-chlorophyll waters of the Northeast Pacific
(Hamme et al., 2010). Climate variability can drive pronounced changes in NPP (Chavez et al.,
2011), such as from El Niño to La Niña transitions in Equatorial Pacific, when vertical nutrient and
trace element supply are enhanced (Chavez et al., 1999).
Multi-year time series records of NPP have been used to assess spatial trends in NPP in recent
decades. Behrenfeld et al. (2006), using satellite data, reported a prolonged and sustained global
NPP decrease of 190 × 1012 g C yr–1, for the period 1999–2005—an annual reduction of 0.57%
of global NPP. In contrast, a time series of directly measured NPP between 1988 and 2007 by
Saba et al. (2010) (i.e., in situ incubations using the radiotracer 14C-bicarbonate) revealed an
increase (2% yr–1) in NPP for two low-latitude open ocean sites. This discrepancy between in situ
and remotely sensed NPP trends points to uncertainties in either the methodology used and/
or the extent to which discrete sites are representative of oceanic provinces (Saba et al., 2010,
2011). Modeling studies have subsequently revealed that the <15-year archive of satellite-
Cross-Chapter Box
Net Primary Production in the Ocean
134
PP
Nutrient
recycling
Nutrients
Trace metals
Euphotic zone (0–100 m)
Upwelling
Vertical mixing
Stratification
(a)
Light
Zooplankton
Microbes
NPP (g C m² y¹)
300 250 200 150 100 50 0
(b)
Latitude
Season
Cloud cover
Figure PP-1 |
(a) Environmental factors controlling Net Primary Production (NPP). NPP is controlled mainly by three basic processes: (1) light conditions in the surface ocean, that
is, the photic zone where photosynthesis occurs; (2) upward flux of nutrients and micronutrients from underlying waters into the photic zone, and (3) regeneration of nutrients and
micronutrients via the breakdown and recycling of organic material before it sinks out of the photic zone. All three processes are influenced by physical, chemical, and biological
processes and vary across regional ecosystems. In addition, water temperature strongly influences the upper rate of photosynthesis for cells that are resource-replete. Predictions of
alteration of primary productivity under climate change depend on correct parameterizations and simulations of each of these variables and processes for each region. (b) Annual
composite map of global areal NPP rates (derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite climatology from 2003–2012; NPP was calculated
with the Carbon-based Productivity Model (CbPM; Westberry et al., 2008)). Overlaid is a grid of (thin black lines) that represent 51 distinct global ocean biogeographical provinces
(after Longhurst, 1998 and based on Boyd and Doney, 2002). The characteristics and boundaries of each province are primarily set by the underlying regional ocean physics and
chemistry. White areas = no data. (Figure courtesy of Toby Westberry (OSU) and Ivan Lima (WHOI), satellite data courtesy of NASA Ocean Biology Processing Group.)
1
3
3
2
Copepod pellets
Microzooplankton
mini-pellets
Particles
Coccolithophorids
Diatoms
Other
Phytoplankton
Copepods
Plankton
Temperature
PP
Net Primary Production in the Ocean
Cross-Chapter Box
135
Arrigo, K.R. and G.L. van Dijken, 2011: Secular trends in Arctic Ocean net primary production. Journal of Geophysical Research, 116(C9), C09011,
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trends in contemporary ocean productivity. Nature, 444(7120), 752-755.
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References
derived NPP is insufficient to distinguish climate-change mediated shifts in NPP from those driven by natural climate variability (Henson et al.,
2010; Beaulieu et al., 2013). Although multi-decadal, the available time series of oceanic NPP measurements are also not of sufficient duration
relative to the time scales of longer-term climate variability modes as for example Atlantic Multi-decadal Oscillation (AMO), with periodicity of
60-70 years, Figure 6-1). Recent attempts to synthesize longer (i.e., centennial) records of chlorophyll as a proxy for phytoplankton stocks (e.g.,
Boyce et al., 2010) have been criticized for relying on questionable linkages between different proxies for chlorophyll over a century of records
(e.g., Rykaczewski and Dunne, 2011).
Models in which projected climate change alters the environmental drivers of NPP provide estimates of spatial changes and of the rate of
change of NPP. For example, four global coupled climate–ocean biogeochemical Earth System Models (WGI AR5 Chapter 6) projected an
increase in NPP at high latitudes as a result of alleviation of light and temperature limitation of NPP, particularly in the high-latitude biomes
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differ substantially. This raises concerns as to which aspect(s) of the different model NPP parameterizations are responsible for driving regional
differences in NPP, and moreover, how accurate model projections are of global NPP.
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scenarios (medium confidence; SRES A2 or RCPs 6.0, 8.5, Sections 6.3.4, 6.5.1), paralleled by an increase in NPP at high latitudes and
a decrease in the tropics (medium confidence). However, there is limited evidence and low agreement on the direction, magnitude and
differences of a change of NPP in various ocean regions and coastal waters projected by 2100 (low confidence).
Cross-Chapter Box
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This cross-chapter box should be cited as:
... The net primary production (NPP) (the focus of the study) is the rate of photosynthesis, carbon fixation minus the percentage of carbon used in the cellular respiration process and cellular construction by selffeeding plankton and benthic flora (Boyd et al., 2014). ...
... There are several environmental factors spatial and temporal that affect the net primary production (Field et al., 1988), of which: light, micronutrients, carbon dioxide and temperature. These factors were affected in turn by changes in the surrounding environment and atmosphere (clouds), the presence of sea ice and water mixing processes caused by wind, waves and water currents in addition to temperature changes (Boyd et al., 2014). ...
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Monthly study was conducted on the net primary productivity and some environmental factors like water temperature, pH, salinity, conductivity, turbidity, light penetration, total suspended solids, total dissolved and alkaline substances, Chl.-a, dissolved oxygen in addition to some Nutrients like NO3, NO2, PO4 and SiO2, were studied in the areas near Umm Qasr Port and near Buoy 17, in addition to the Basra oil port area in the Iraqi coastal waters. The current study showed that the values of primary productivity ranged from 15.9-98.55 Cmg/l, and the pH and alkalinity were within the ranges prevailing in the Iraqi coastal waters and the temperature values were within their annual rates as they ranged from 14-34°C, while the values of the pH and alkalinity were within the ranges prevailing in the Iraqi coastal waters, the recorded values of light penetration were 14-250cm, while the turbidity values in the third station decreased, high values were recorded in the first and second stations and this is the case in the TSS and TDS values as well.
... Evidence is increasing that the ocean's oxygen content is declining (Oschlies et al., 2018). AR5 did not come to a final conclusion with regard to potential long-term changes in ocean productivity due to short observational records and divergent scientific evidence (Boyd et al., 2014;Section 5.2.2). Ocean acidification and deoxygenation are projected to continue over the next century with high confidence (Sections 3.2.2.3, 5.2.2). 1 84 ...
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Framing and Context of the Report Chapter 1 Executive Summary This special report assesses new knowledge since the IPCC 5th Assessment Report (AR5) and the Special Report on Global Warming of 1.5oC (SR15) on how the ocean and cryosphere have and are expected to change with ongoing global warming, the risks and opportunities these changes bring to ecosystems and people, and mitigation, adaptation and governance options for reducing future risks. Chapter 1 provides context on the importance of the ocean and cryosphere, and the framework for the assessments in subsequent chapters of the report. All people on Earth depend directly or indirectly on the ocean and cryosphere. The fundamental roles of the ocean and cryosphere in the Earth system include the uptake and redistribution of anthropogenic carbon dioxide and heat by the ocean, as well as their crucial involvement of in the hydrological cycle. The cryosphere also amplifies climate changes through snow, ice and permafrost feedbacks. Services provided to people by the ocean and/or cryosphere include food and freshwater, renewable energy, health and wellbeing, cultural values, trade and transport. {1.1, 1.2, 1.5} Sustainable development is at risk from emerging and intensifying ocean and cryosphere changes. Ocean and cryosphere changes interact with each of the United Nations Sustainable Development Goals (SDGs). Progress on climate action (SDG 13) would reduce risks to aspects of sustainable development that are fundamentally linked to the ocean and cryosphere and the services they provide (high confidence1). Progress on achieving the SDGs can contribute to reducing the exposure or vulnerabilities of people and communities to the risks of ocean and cryosphere change (medium confidence). {1.1} Communities living in close connection with polar, mountain, and coastal environments are particularly exposed to the current and future hazards of ocean and cryosphere change. Coasts are home to approximately 28% of the global population, including around 11% living on land less than 10 m above sea level. Almost 10% of the global population lives in the Arctic or high mountain regions. People in these regions face the greatest exposure to ocean and cryosphere change, and poor and marginalised people here are particularly vulnerable to climate-related hazards and risks (very high confidence). The adaptive capacity of people, communities and nations is shaped by social, political, cultural, economic, technological, institutional, geographical and demographic factors. {1.1, 1.5, 1.6, Cross-Chapter Box 2 in Chapter 1} Ocean and cryosphere changes are pervasive and observed from high mountains, to the polar regions, to coasts, and into the deep ocean. AR5 assessed that the ocean is warming (0 to 700 m: virtually certain2; 700 to 2,000 m: likely), sea level is rising (high confidence), and ocean acidity is increasing (high confidence). Most glaciers are shrinking (high confidence), the Greenland and Antarctic ice sheets are losing mass (high confidence), sea ice extent in the Arctic is decreasing (very high confidence), Northern Hemisphere snow cover is decreasing (very high confidence), and permafrost temperatures are increasing (high confidence). Improvements since AR5 in observation systems, techniques, reconstructions and model developments, have advanced scientific characterisation and understanding of ocean and cryosphere change, including in previously identified areas of concern such as ice sheets and Atlantic Meridional Overturning Circulation (AMOC). {1.1, 1.4, 1.8.1} Evidence and understanding of the human causes of climate warming, and of associated ocean and cryosphere changes, has increased over the past 30 years of IPCC assessments (very high confidence). Human activities are estimated to have caused approximately 1.0oC of global warming above pre-industrial levels (SR15). Areas of concern in earlier IPCC reports, such as the expected acceleration of sea level rise, are now observed (high confidence). Evidence for expected slow-down of AMOC is emerging in sustained observations and from long-term palaeoclimate reconstructions (medium confidence), and may be related with anthropogenic forcing according to model simulations, although this remains to be properly attributed. Significant sea level rise contributions from Antarctic ice sheet mass loss (very high confidence), which earlier reports did not expect to manifest this century, are already being observed. {1.1, 1.4} Ocean and cryosphere changes and risks by the end-of-century (2081–2100) will be larger under high greenhouse gas emission scenarios, compared with low emission scenarios (very high confidence). Projections and assessments of future climate, ocean and cryosphere changes in the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) are commonly based on coordinated climate model experiments from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced with Representative Concentration Pathways (RCPs) of future radiative forcing. Current emissions continue to grow at a rate consistent with a high emission future without effective climate change mitigation policies (referred to as RCP8.5). The SROCC assessment contrasts this high greenhouse gas emission future with a low greenhouse gas emission, high mitigation future (referred to as RCP2.6) that gives a two in three chance of limiting warming by the end of the century to less than 2oC above pre-industrial. {Cross-Chapter Box 1 in Chapter 1} 1 1 2 In this report, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, for example, medium confidence. For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see Section 1.9.2 and Figure 1.4 for more details). In this report, the following terms have been used to indicate the assessed likelihood of an outcome or a result: Virtually certain 99–100% probability, Very likely 90–100%, Likely 66–100%, About as likely as not 33–66%, Unlikely 0–33%, Very unlikely 0–10%, and Exceptionally unlikely 0–1%. Additional terms (Extremely likely: 95–100%, More likely than not >50–100%, and Extremely unlikely 0–5%) may also be used when appropriate. Assessed likelihood is typeset in italics, for example, very likely (see Section 1.9.2 and Figure 1.4 for more details). This Report also uses the term ‘likely range’ to indicate that the assessed likelihood of an outcome lies within the 17–83% probability range. 75 1 Characteristics of ocean and cryosphere change include thresholds of abrupt change, long-term changes that cannot be avoided, and irreversibility (high confidence). Ocean warming, acidification and deoxygenation, ice sheet and glacier mass loss, and permafrost degradation are expected to be irreversible on time scales relevant to human societies and ecosystems. Long response times of decades to millennia mean that the ocean and cryosphere are committed to long-term change even after atmospheric greenhouse gas concentrations and radiative forcing stabilise (high confidence). Ice-melt or the thawing of permafrost involve thresholds (state changes) that allow for abrupt, nonlinear responses to ongoing climate warming (high confidence). These characteristics of ocean and cryosphere change pose risks and challenges to adaptation. {1.1, Box 1.1, 1.3} Societies will be exposed, and challenged to adapt, to changes in the ocean and cryosphere even if current and future efforts to reduce greenhouse gas emissions keep global warming well below 2oC (very high confidence). Ocean and cryosphere-related mitigation and adaptation measures include options that address the causes of climate change, support biological and ecological adaptation, or enhance societal adaptation. Most ocean-based local mitigation and adaptation measures have limited effectiveness to mitigate climate change and reduce its consequences at the global scale, but are useful to implement because they address local risks, often have co-benefits such as biodiversity conservation, and have few adverse side effects. Effective mitigation at a global scale will reduce the need and cost of adaptation, and reduce the risks of surpassing limits to adaptation. Ocean-based carbon dioxide removal at the global scale has potentially large negative ecosystem consequences. {1.6.1, 1.6.2, Cross-Chapter Box 2 in Chapter 1} The scale and cross-boundary dimensions of changes in the ocean and cryosphere challenge the ability of communities, cultures and nations to respond effectively within existing governance frameworks (high confidence). Profound economic and institutional transformations are needed if climate-resilient development is to be achieved (high confidence). Changes in the ocean and cryosphere, the ecosystem services that they provide, the drivers of those changes, and the risks to marine, coastal, polar and mountain ecosystems, occur on spatial and temporal scales that may not align within existing governance structures and practices (medium confidence). This report highlights the requirements for transformative governance, international and transboundary cooperation, and greater empowerment of local communities in the governance of the ocean, coasts, and cryosphere in a changing climate. {1.5, 1.7, Cross-Chapter Box 2 in Chapter 1, Cross-Chapter Box 3 in Chapter 1} Robust assessments of ocean and cryosphere change, and the development of context-specific governance and response options, depend on utilising and strengthening all available knowledge systems (high confidence). Scientific knowledge from observations, models and syntheses provides global to local scale understandings of climate change (very high confidence). Indigenous knowledge (IK) and local knowledge (LK) provide context-specific and socio-culturally relevant understandings for effective responses and policies (medium confidence). Education and climate literacy enable climate action and adaptation (high confidence). {1.8, Cross-Chapter Box 4 in Chapter 1} Long-term sustained observations and continued modelling are critical for detecting, understanding and predicting ocean and cryosphere change, providing the knowledge to inform risk assessments and adaptation planning (high confidence). Knowledge gaps exist in scientific knowledge for important regions, parameters and processes of ocean and cryosphere change, including for physically plausible, high impact changes like high end sea level rise scenarios that would be costly if realised without effective adaptation planning and even then may exceed limits to adaptation. Means such as expert judgement, scenario building, and invoking multiple lines of evidence enable comprehensive risk assessments even in cases of uncertain future ocean and cryosphere changes. {1.8.1, 1.9.2; Cross-Chapter Box 5 in Chapter 1}
... Ocean production is about 50 billion tonnes of C [56] on 360 million km 2 . That is: oceans are underproducing relative to land. ...
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This supplement provides additional background information for a paper entitled Restoring pre-industrial CO2 levels while achieving Sustainable Development Goals, which is currently undergoing peer review.
... Evidence is increasing that the ocean's oxygen content is declining (Oschlies et al., 2018). AR5 did not come to a final conclusion with regard to potential long-term changes in ocean productivity due to short observational records and divergent scientific evidence (Boyd et al., 2014;Section 5.2.2). Ocean acidification and deoxygenation are projected to continue over the next century with high confidence (Sections 3.2.2.3, 5.2.2). 1 84 ...
... Only the Primary Productivity is not available in a numerical model and must be given to the users. This parameter is not uniform at the surface of the oceans (Boyd et al., 2014) and different weights (or frequencies of appearance) must be applied on its values regarding their statistical occurrence. No data-base or computational methods exist at this day to estimate Paleo-Primary Productivities so present-day data from the literature (Longhurst et al., 1995) have been used. ...
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Basin modelling encompasses a broad range of related geological disciplines used to represent and describe how sedimentary basins were formed and evolved over time. It is often employed, but not solely, to appraise their potential for hydrocarbons exploration and production. Regarding petroleum systems, discerning and possessing the ability to precisely quantify the uncertainties associated to the generation and accumulation of oil and gas are the keys to deliver relevant and exhaustive analysis since no model or interpretation can at present perfectly mirror reality. To achieve this, classical techniques, as Monte Carlo, rely on statistical concepts necessiting important computing power as they require thousands of simulations. Modern optimized algorithms combining statistical concepts such as Latin Hypercube Sampling and machine learning methods can significantly downplay the number of simulations and thus the computing time required to generate realistic alternative probabilistic outcomes. They turn out to be particularly effective when mastered but require expertise across numerous scientific fields further to an extensive basin modelling experience. Thence, they remain used by a limited community of experts, often limited to R&D centers, rather than being widely adopted in exploration practices. In addition, plenty of these experts will retire in the coming years without necessarily being able to pass the torch and too few geoscientists are adequately trained to master these methods, facing the industry with a dilemma. In this paper, the objective is to present an innovative workflow for risk and uncertainty analysis in basin modelling. By using already developed advanced statistics optimization approaches and combining it with a new parametrization procedure based on well-known geological concepts instead of independent variables, this new workflow is designed to reach a wider and less experienced community while downsizing computing time and remaining agile and pertinent. In illustration of the general parametrization procedure, three new specific methodologies to assess the richness, the reactivity and the thickness of a source-rock are described following the philosophy of the workflow. They have been tested on a real case study over the Levantine Basin and present promising results as they required 50 times fewer simulations than Monte Carlo approach to provide results coherent with expected geological contexts and physical behaviors of the basin.
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The ultimate cause(s) of the end-Permian mass extinction (~252 Ma ago) has been disputed. A complex interplay of various effects, rather than a single, universal killing mechanism, were most likely involved. Climate warming as consequence of greenhouse gas emissions by contemporaneous Siberian Traps volcanism is widely accepted as an initial trigger. Synergetic effects of global warming include increasing stratification of the oceans, inefficient water column mixing, and eventually low marine primary productivity culminating in a series of consequences for higher trophic levels. To explore this scenario in the context of the end-Permian mass extinction, we investigated sedimentary total organic carbon, phosphorus speciation as well as nickel concentrations in two low-latitude Tethyan carbonate sections spanning the Permian-Triassic transition. Total organic carbon, reactive phosphorus and nickel concentrations all decrease in the latest Permian and are low during the Early Triassic, pointing to a decline in primary productivity within the Tethyan realm. We suggest that the productivity collapse started in the upper C. yini conodont Zone, approximately 30 ka prior to the main marine extinction interval. Reduced primary productivity would have resulted in food shortage and thus may serve as explanation for pre-mass extinction perturbations among marine heterotrophic organisms.
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Polovina, J. J., Dunne, J. P., Woodworth, P. A., and Howell, E. A. 2011. Projected expansion of the subtropical biome and contraction of the temperate and equatorial upwelling biomes in the North Pacific under global warming. – ICES Journal of Marine Science, 68: 986–995. A climate model that includes a coupled ocean biogeochemistry model is used to define large oceanic biomes in the North Pacific Ocean and describe their changes over the 21st century in response to the IPCC Special Report on Emission Scenario A2 future atmospheric CO2 emissions scenario. Driven by enhanced stratification and a northward shift in the mid-latitude westerlies under climate change, model projections demonstrated that between 2000 and 2100, the area of the subtropical biome expands by ∼30% by 2100, whereas the area of temperate and equatorial upwelling (EU) biomes decreases by ∼34 and 28%, respectively, by 2100. Over the century, the total biome primary production and fish catch is projected to increase by 26% in the subtropical biome and decrease by 38 and 15% in the temperate and the equatorial biomes, respectively. Although the primary production per unit area declines slightly in the subtropical and the temperate biomes, it increases 17% in the EU biome. Two areas where the subtropical biome boundary exhibits the greatest movement is in the northeast Pacific, where it moves northwards by as much as 1000 km per 100 years and at the equator in the central Pacific, where it moves eastwards by 2000 km per 100 years. Lastly, by the end of the century, there are projected to be more than 25 million km² of water with a mean sea surface temperature of 31°C in the subtropical and EU biomes, representing a new thermal habitat. The projected trends in biome carrying capacity and fish catch suggest resource managers might have to address long-term trends in fishing capacity and quota levels.
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Resolution of the nitrogen (N) cycle in the marine environment requires an accurate assessment of dinitrogen (N2) fixation. We present here an update on progress in conducting field measurements of acetylene reduction (AR) and 15N2 tracer assimilation in the oligotrophic North Pacific Subtropical Gyre (NPSG). The AR assay was conducted on discrete seawater samples using a headspace analysis system, followed by quantification of ethylene (C2H4) with a reducing compound photodetector. The rates of C2H4 production were measurable for nonconcentrated seawater samples after an incubation period of 3 to 4 h. The 15N2 tracer measurements compared the addition of 15N2 as a gas bubble and dissolved as 15N2 enriched seawater. On all sampling occasions and at all depths, a 2- to 6-fold increase in the rate of 15N2 assimilation was measured when 15N2-enriched seawater was added to the seawater sample compared to the addition of 15N2 as a gas bubble. In addition, we show that the 15N2-enriched seawater can be prepared prior to its use with no detectable loss (<1.7%) of dissolved 15N2 during 4 weeks of storage, facilitating its use in the field. The ratio of C2H4 production to 15N2 assimilation varied from 7 to 27 when measured simultaneously in surface seawater samples. Collectively, the modifications to the AR assay and the 15N2 assimilation technique present opportunities for more accurate and high frequency measurements (e.g., diel scale) of N2 fixation, providing further insight into the contribution of different groups of diazotrophs to the input of N in the global oceans.
Article
Current coupled ocean-atmosphere model (COAM) projections of future oceanic anthropogenic carbon uptake suggest reduced rates due to surface warming, enhanced stratification, and slowed thermohaline overturning. Such models rely on simple, bulk biogeochemical parameterisations, whereas recent ocean observations indicate that floristic shifts may be induced by climate variability, are widespread, complex, and directly impact biogeochemical cycles. We present a strategy to incorporate ecosystem function in COAM's and to evaluate the results in relation to region-specific ecosystem dynamics and interannual variability using a template of oceanic biogeographical provinces. Illustrative simulations for nitrogen fixers with an off-line multi-species, functional group model suggest significant changes by the end of this century in ecosystem structure, with some of the largest regional impacts caused by shifts in the areal extent of biomes.
Book
This book presents an in-depth discussion of the biological and ecological geography of the oceans. It synthesizes locally restricted studies of the ocean to generate a global geography of the vast marine world. Based on patterns of algal ecology, the book divides the ocean into four primary compartments, which are then subdivided into secondary compartments. *Includes color insert of the latest in satellite imagery showing the world's oceans, their similarities and differences *Revised and updated to reflect the latest in oceanographic research *Ideal for anyone interested in understanding ocean ecology -- accessible and informative.
Article
We coupled dinitrogen (N2) fixation rate estimates with molecular biological methods to determine the activity and abundance of diazotrophs in coastal waters along the temperate North American Mid-Atlantic continental shelf during multiple seasons and cruises. Volumetric rates of N2 fixation were as high as 49.8 nmol N L−1 d−1 and areal rates as high as 837.9 µmol N m−2 d−1 in our study area. Our results suggest that N2 fixation occurs at high rates in coastal shelf waters that were previously thought to be unimportant sites of N2 fixation and so were excluded from calculations of pelagic marine N2 fixation. Unicellular N2-fixing group A cyanobacteria were the most abundant diazotrophs in the Atlantic coastal waters and their abundance was comparable to, or higher than, that measured in oceanic regimes where they were discovered. High rates of N2 fixation and the high abundance of diazotrophs along the North American Mid-Atlantic continental shelf highlight the need to revise marine N budgets to include coastal N2 fixation. Integrating areal rates of N2 fixation over the continental shelf area between Cape Hatteras and Nova Scotia, the estimated N2 fixation in this temperate shelf system is about 0.02 Tmol N yr−1, the amount previously calculated for the entire North Atlantic continental shelf. Additional studies should provide spatially, temporally, and seasonally resolved rate estimates from coastal systems to better constrain N inputs via N2 fixation from the neritic zone.
Article
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