Bioavailable atmospheric phosphorous supply to the global ocean: a 3-D global modelling study (original) (raw)
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Phosphorus associations in aerosols: What can they tell us about P bioavailability?
Marine Chemistry, 2010
Phosphorus (P) in aerosols can originate from multiple sources (mineral dust, biomass burning, fuel emissions) and can be associated with multiple phases including various minerals, organic matter and P adsorbed on particle surfaces. These associations will greatly impact the solubility of P in an aerosol sample and thus determine the bioavailability of P from atmospheric deposition to oceanic ecosystems. Here we use a sequential leaching extraction to determine the distribution of P within different operationally defined fractions in aerosol samples reaching the Gulf of Aqaba from different air mass trajectories and at different seasons. We found that on average 40% of the P in aerosols is associated with the "authigenic" fraction (soluble in acetic acid) which is unlikely to dissolve in seawater and become bioavailable. Another 15% is associated with each the HCl-"detrital" and insoluble organic matter components that are also not readily bioavailable. Only 15-30% of P is associated with phases that are water soluble or that are relatively soluble oxide phases that may be bioavailable for organisms. We did not find a consistent relationship between the distribution of P in the various phases and air-mass back trajectory or season but a distinct and strong positive correlation was observed between metals associated with anthropogenic sources such as Zn and Ni and the extractable water soluble P fraction. This suggests that anthropogenic P sources are more soluble and bioavailable than mineral sources even though most of the P in aerosols in this region is in the mineral phase. These results have implications for determining how changes in atmospheric input of P to the ocean related to urban development and anthropogenic (wood and fuel burning) activities may impact marine ecosystems.
Proceedings of the National Academy of Sciences of the United States of America, 2016
Acidification of airborne dust particles can dramatically increase the amount of bioavailable phosphorus (P) deposited on the surface ocean. Experiments were conducted to simulate atmospheric processes and determine the dissolution behavior of P compounds in dust and dust precursor soils. Acid dissolution occurs rapidly (seconds to minutes) and is controlled by the amount of H(+) ions present. For H(+) < 10(-4) mol/g of dust, 1-10% of the total P is dissolved, largely as a result of dissolution of surface-bound forms. At H(+) > 10(-4) mol/g of dust, the amount of P (and calcium) released has a direct proportionality to the amount of H(+) consumed until all inorganic P minerals are exhausted and the final pH remains acidic. Once dissolved, P will stay in solution due to slow precipitation kinetics. Dissolution of apatite-P (Ap-P), the major mineral phase in dust (79-96%), occurs whether calcium carbonate (calcite) is present or not, although the increase in dissolved P is great...
Global Biogeochemical Cycles, 2008
1] A worldwide compilation of atmospheric total phosphorus (TP) and phosphate (PO 4 ) concentration and deposition flux observations are combined with transport model simulations to derive the global distribution of concentrations and deposition fluxes of TP and PO 4 . Our results suggest that mineral aerosols are the dominant source of TP on a global scale (82%), with primary biogenic particles (12%) and combustion sources (5%) important in nondusty regions. Globally averaged anthropogenic inputs are estimated to be $5 and 15% for TP and PO 4 , respectively, and may contribute as much as 50% to the deposition over the oligotrophic ocean where productivity may be phosphorus-limited. There is a net loss of TP from many (but not all) land ecosystems and a net gain of TP by the oceans (560 Gg P a À1 ). More measurements of atmospheric TP and PO 4 will assist in reducing uncertainties in our understanding of the role that atmospheric phosphorus may play in global biogeochemistry. Citation: Mahowald, N., et al. (2008), Global distribution of atmospheric phosphorus sources, concentrations and deposition rates, and anthropogenic impacts, Global Biogeochem. Cycles, 22, GB4026,
Atmospheric acidification of mineral aerosols: a source of bioavailable phosphorus for the oceans
Atmospheric Chemistry and Physics, 2011
Primary productivity of continental and marine ecosystems is often limited or co-limited by phosphorus. Deposition of atmospheric aerosols provides the major external source of phosphorus to surface waters. However, only a fraction of deposited aerosol phosphorus is water soluble and available for uptake by phytoplankton. We propose that 5 atmospheric acidification of aerosols is a prime mechanism producing soluble phosphorus from soil-derived minerals. Acid mobilization is expected to be pronounced where polluted and dust-laden air masses mix. Our hypothesis is supported by the soluble compositions and reconstructed pH values for atmospheric particulate matter samples collected over a 5-year period at Finokalia, Crete. At least tenfold increase 10 in soluble phosphorus is observed when Saharan soil and dust were acidified in laboratory experiments which simulate atmospheric conditions. Aerosol acidification links bioavailable phosphorus supply to anthropogenic and natural acidic gas emissions, and may be a key regulator of ocean biogeochemistry. Pytkowicz, 1977). Combined with the short transit times of mineral aerosols through 6165
Environmental Science & Technology, 2012
Atmospheric P solubility affects the amount of P available for phytoplankton in the surface ocean, yet our understanding of the timing and extent of atmospheric P solubility is based on short-term leaching experiments where conditions may differ substantially from the surface ocean. We conducted longer-term dissolution experiments of atmospheric aerosols in filtered seawater, and found up to 9-fold greater dissolution of P after 72 h compared to instantaneous leaching. Samples rich in anthropogenic materials released dissolved inorganic P (DIP) faster than mineral dust. To gauge the effect of biota on the fate of atmospheric P, we conducted field incubations with aerosol samples collected in the Sargasso Sea and Red Sea. In the Sargasso Sea phytoplankton were not P limited, and biological activity enhanced DIP release from aerosols, and aerosols induced biological mineralization of dissolved organic P in seawater, leading to DIP accumulation. However, in the Red Sea where phytoplankton were colimited by P and N, soluble P was rapidly consumed by phytoplankton following aerosol enrichment. Our results suggest that atmospheric P dissolution could continue over multiple days once reaching the surface ocean, and that previous estimates of atmospheric P deposition may underestimate the contribution from this source.
Tellus B, 2012
The continental outflow from the Indo-Gangetic Plain and Southeast Asia, during the late NE monsoon (JanuaryÁMarch), dominates the transport of chemical constituents to the marine atmospheric boundary layer (MABL) of the Bay of Bengal (BoB). During the rest of the year, prevailing wind regimes and meteorological conditions do not favour the atmospheric transport of continental products. Here we report on the spatiotemporal variability of inorganic phosphorous (P Inorg 0PO 3À 4 ) in the MABL and its dry-deposition flux to the surface BoB. On the basis of the abundance of P Inorg in PM 2.5 (0.1Á0.8 nmol m (3 ) and PM 10 (0.3Á2.8 nmol m (3 ), we document its dominant occurrence in the coarse mode (D a ]2.5 mm). The analytical data also provide evidence for the chemical processing of mineral dust by acidic species and mobilisation of P Inorg during the long-range atmospheric transport. However, significantly high P Inorg /non-sea-salt Ca 2' ratios over the BoB suggest dominant contribution from anthropogenic sources (fertilisers and biomass burning emissions). P Inorg concentration over the Arabian Sea is about 4 to 5 times lower and is primarily associated with the mineral dust from desert regions. The dry-deposition flux of P Inorg to the BoB varies by one order of magnitude (0.5Á 5.0 mmol P m (2 d (1 ; Av: 0.02 Tg P yr (1 ). These results have implications to the air-sea deposition of phosphorous over oceanic regions downwind of the pollution sources and impact on the biogeochemistry of surface waters.
Phosphorus distribution in sinking oceanic particulate matter
Marine Chemistry, 2005
Despite the recognition of the importance of phosphorus (P) in regulating marine productivity in some modern oceanic systems and over long timescales, the nature of particulate P within the ocean is not well understood. We analyzed P concentration in particulate matter from sediment traps and selected core tops from a wide range of oceanic regimes: open ocean environments (Equatorial Pacific, North Central Pacific), polar environments (Ross Sea, Palmer Deep), and coastal environments (Northern California Coast, Monterey Bay, Point Conception). These sites represent a range of productivity levels, temporal (seasonal to annual) distributions, and trap depths (200-4400 m). P associations were identified using an operationally defined sequential extraction procedure. We found that P in the sediment traps is typically composed of reactive P components including acid-insoluble organic P (~40%), authigenic P (~25%), and oxide associated and/or labile P (~21%), with lesser proportions of non-reactive detrital P depending on location (~13%). The concentrations and fluxes of all particulate P components except detrital P decrease or remain constant with depth between the shallowest and the deepest sediment traps, indicating some regeneration of reactive P components. Transformation from more labile forms of P to authigenic P is evident between the deepest traps and core top sediments. Although for most sites the magnitudes of reactive P fluxes are seasonally variable and productivity dependent, the fractional associations of reactive P are independent of season. We conclude that P is transported from the upper water column to the sediments in various forms previously considered unimportant. Thus, acid-insoluble organic P measurements (typically reported as particulate organic P) likely underestimate biologically related particulate P, because they do not include the labile, oxide-associated, or authigenic P fractions that often are or recently were biologically related. Organic C to reactive P ratios are typically higher than Redfield Ratio and are relatively constant with depth below~300 m suggesting that preferential regeneration of P relative to C occurs predominantly at shallow depths in the water column, but not deeper in the water column (N 300 m). The view of P cycling in the oceans should be revised (1) to include P fractions other than acid-soluble organic P as important carriers of reactive P in rapidly sinking particles, (2) to include the efficient transformation of labile forms of P 0304-4203/$ -see front matter D (K.L. Faul).
Analysis of Aerosol Phosphorus Delivered to the Mediterranean Sea 1
2014
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, 5 Atlanta, GA 30332-0340, USA. 6 School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst 7 Drive, Atlanta, GA 30332-0340, USA. 8 Foundation for Research and Technology, Hellas, Patras 70013, Greece. 9 University of Crete, Department of Chemistry, Iraklion 71003, Greece. 10 CREAF, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain. 11 Department of Earth & Ocean Sciences & Marine Science Program, University of South 12 Carolina, Columbia, SC 29208, USA. 13 Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA 31411, USA. 14 Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 15 60439, USA. 16 Present address: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, 17 MA 02543, USA. 18 Present Address: Environmental Protection Agency, National Center of Environmental 19 Assessment, Re...
Atmospheric fluxes of organic N and P to the global ocean
Global Biogeochemical Cycles, 2012
ABSTRACT The global tropospheric budget of gaseous and particulate non-methane organic matter (OM) is re-examined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3-dimensional chemistry-transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from ˜3% to 90% (median of ˜35%) of total soluble N in rainwater; soluble OP ranges from ˜20-83% (median of ˜35%) of total soluble phosphorus. The simulations suggest that the global ON cycle has a strong anthropogenic component with ˜45% of the overall atmospheric source (primary and secondary) associated with anthropogenic activities. In contrast, only 10% of atmospheric OP is emitted from human activities. The model-derived present-day soluble ON and OP deposition to the global ocean is estimated to be ˜16 Tg-N/yr and ˜0.35 Tg-P/yr respectively with an order of magnitude uncertainty. Of these amounts ˜40% and ˜6%, respectively, are associated with anthropogenic activities, and 33% and 90% are recycled oceanic materials. Therefore, anthropogenic emissions are having a greater impact on the ON cycle than the OP cycle; consequently increasing emissions may increase P-limitation in the oligotrophic regions of the world&#39;s ocean that rely on atmospheric deposition as an important nutrient source.
GESAMP Working Group 38, The Atmospheric Input of Chemicals to the Ocean
2014
The atmospheric input of chemicals to the ocean is closely related to a number of important global change issues. The increasing input of atmospheric anthropogenic nitrogen species to much of the ocean may cause a low level fertilization of the ocean that could result in an increase in marine 'new' productivity of up to ~3% and thus impact carbon drawdown from the atmosphere. However, the increase in nitrogen inputs are also likely to increase the formation of nitrous oxide in the ocean. The increased emission of this powerful greenhouse gas will partially offset the climate forcing impact resulting from the increase in carbon dioxide drawdown produced by N fertilization. Similarly, much of the oceanic iron, which is a limiting nutrient in many areas of the ocean, originates from the atmospheric input of minerals as a result of the long-range transport of mineral dust from continental regions. The increased supply of soluble phosphorus from atmospheric anthropogenic sources (through large-scale use in fertilizers) may also have a significant impact on surface-ocean biogeochemistry, but estimates are highly uncertain. While it is possible that the inputs of sulphur and nitrogen oxides from the atmosphere can add to the rates of ocean acidification occurring due to rising levels of carbon dioxide, there is too little information on these processes to assess the potential impact. These inputs may be particularly critical in heavily trafficked shipping lanes and in ocean regions proximate to highly industrialized land areas. Other atmospheric substances may also have an impact on the ocean, in particular lead, cadmium, and POPs. GESAMP initiated Working Group 38, The Atmospheric Input of Chemicals to the Ocean, to address these issues. Working Group 38 was initially formed to address the following Terms of Reference: 1) Assess the need for the development of new model and measurement products for improving our understanding of the impacts of the atmospheric deposition of nitrogen species and dust (iron) to the ocean; 2) Review the present information on the atmospheric deposition of phosphorus species to both the marine and terrestrial environments, considering both natural and anthropogenic sources, and evaluate the impact of atmospheric phosphorus deposition on marine and terrestrial ecosystems. Consider whether such a review of any other substance would be useful. 3) Work with the WMO Sand and Dust Storm Warning and Assessment System (SDS-WAS) and with the WMO Precipitation Chemistry Data Synthesis and Community Project to evaluate the needs of the marine community and assist in clearly articulating them in the development of these WMO efforts. Additional tasks were later developed for the working group, in particular to more specifically elaborate the role of minerals carried by the dust which is responsible for marine production and to achieve more detailed and more specific description of the atmospheric transport and deposition process of iron-and phosphorus-carried minerals. To this end, the activities of Working Group 38 were extended with the aim of bringing together the SDS-WAS and GESAMP scientific communities and, as a result of their joint effort, to evaluate the following topics: Topic 1 Improving the quantitative estimates of the geographical distribution of the transport and deposition of mineral matter and its content to the ocean. Topic 2 Developing case-studies of dust/Fe/P input to the ocean and the resultant marine response utilizing SDS-WAS transport modelling, remote-sensing, in-situ observations, and ocean biogeochemical modelling. Topic 3 Specifying test-bed regions for joint studies of the transport and deposition to the ocean of mineral matter. Charges 1) and 2) above were addressed by developing separate peer-reviewed scientific papers in the areas of phosphorus, nitrogen, sulphur, iron and organic matter deposition from the atmosphere to the ocean. Summaries of these papers are presented in this report. Charge 3) was addressed by the development of two advisory letter reports to the World Meteorological Organization in the areas of dust deposition to the ocean and precipitation chemistry over the ocean, and they are presented in this report. Topics 1, 2, and 3 were discussed in detail at a joint meeting of GESAMP WG38 and SDS-WAS, and separate analyses on each of these topics were developed and are presented in this report. The results of the deliberations of this working group have significant implications for policy-makers. Atmospheric mineral dust often originates from very specific source areas and is then transported over long distances, influencing the climate and chemistry of the atmosphere on local, regional, and global scales. It has implications for Executive Summary ii human health, visibility, and climate. It also provides essential components for ocean fertility, primarily the micronutrient iron. Measurements on various times scales have suggested strong correlations of dust emissions, transport and deposition with climate change. Given the importance of dust in the earth system, including deposition to the oceans, it is unfortunate that it represents one of the primary uncertainties in future climate change scenarios. Policy-makers must become aware of the importance of atmospheric mineral dust and its wide range of environmental impacts. Continued support for research on mineral dust has multiple benefits ranging from improving short-term forecasting to improved understanding of the role of mineral dust in supplying nutrients to the world's oceans. Supplying iron to iron-depleted regions has been proposed as a form of geo-engineering to remove carbon dioxide from the atmosphere. While a discussion of the pros and cons of this approach is beyond the scope of the Working Group, we require a much better understanding of the role of mineral dust and related processes before we can make sound science-based decisions. Absorption by the ocean of gases such as sulphuric and nitric acids will tend to decrease seawater pH which will in turn cause CO2 to be released from the ocean to the atmosphere. This will moderate or cancel out the expected pH drop and concomitantly decrease the effectiveness of the seawater as a sink for carbon dioxide in areas of major strong acid deposition. Thus it is clearly desirable to reduce the emissions of the strong acid precursors SO2 and NOx from shipping and land-based sources so as to improve air quality both locally and regionally, but such reductions will probably have little effect on the pH of seawater. These policy-oriented remarks should be seen in the context of the almost certainty that growth and urban/industrial development for the foreseeable future will be primarily concentrated in coastal and near-coastal areas. This means that control of emissions of acidic gases to the atmosphere from such zones will continue to be a growing area of concern for air quality and of consequent significance for carbon dioxide uptake by affected marine waters. Clearly models are essential to developing an understanding of the processes and impacts of the atmospheric input of chemicals to the ocean. The lack of high quality, harmonized deposition measurements that are needed for model verification is a serious issue. The existing network of WMO GAW sites could play a critical role in providing for extended measurements pertaining to nutrient and contaminant deposition and the related ocean biological and physical parameters. However, additional atmospheric sampling sites, especially in the Southern Hemisphere, are necessary. Therefore continuing long-term observations remains of highest priority for policy-makers, both for improving models and monitoring future changes. Finally, institutional support for assessment activities, intercomparisons, and appropriate identification and documentation of models and measurements, remains a high priority. This support is necessary to ensure an improved understanding of the role of dust both now and on longer time scales.