The atmospheric input of trace species to the world ocean

Abstract

Over the past decade it has become apparent that the atmosphere is a significant pathway for the transport of many natural and pollutant materials from the continents to the ocean. The atmospheric input of many of these species can have an impact (either positive or negative) on biological processes in the sea and on marine chemical cycling. For example, there is now evidence that the atmosphere may be an important transport path for such essential nutrients as iron and nitrogen in some regions. In this report we assess current data in this area, develop global scale estimates of the atmospheric fluxes of trace elements, mineral aerosol, nitrogen species, and synthetic organic compounds to the ocean; and compare the atmospheric input rates of these substances to their input via rivers. Trace elements considered were Pb, Cd, Zn, Cu, Ni, As, Hg, Sn, Al, Fe, Si, and P. Oxidized and reduced forms of nitrogen were considered, including nitrate and ammonium ions and the gaseous species NO, NO2, HNO3, and NH3. Synthetic organic compounds considered included polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs), DDTs, chlordane, dieldrin, and hexachlorobenzenes (HCBs). Making this assessment was difficult because there are very few actual measurements of deposition rates of these substances to the ocean. However, there are considerably more data on the atmospheric concentrations of these species in aerosol and gaseous form. Mean concentration data for 10° × 10° ocean areas were determined from the available concentration data or from extrapolation of these data into other regions. These concentration distributions were then combined with appropriate exchange coefficients and precipitation fields to obtain the global wet and dry deposition fluxes. Careful consideration was given to atmospheric transport processes as well as to removal mechanisms and the physical and physicochemical properties of aerosols and gases. Only annual values were calculated. On a global scale atmospheric inputs are generally equal to or greater than riverine inputs, and for most species atmospheric input to the ocean is significantly greater in the northern hemisphere than in the southern hemisphere. For dissolved trace metals in seawater, global atmospheric input dominates riverine input for Pb, Cd, and Zn, and the two transport paths are roughly equal for Cu, Ni, As, and Fe. Fluxes and basin‐wide deposition of trace metals are generally a factor of 5‐10 higher in the North Atlantic and North Pacific regions than in the South Atlantic and South Pacific. Global input of oxidized and reduced nitrogen species are roughly equal to each other, although the major fraction of oxidized nitrogen enters the ocean in the northern hemisphere, primarily as a result of pollution sources. Reduced nitrogen species are much more uniformly distributed, suggesting that the ocean itself may be a significant source. The global atmospheric input of such synthetic organic species as HCH,PCBs, DDT, and HCB completely dominates their input via rivers.

Atmospheric P deposition to the subtropical North Atlantic: sources, properties, and relationship to N deposition

“…This ratio was based on measurements of dust in aerosols and rain over the North Atlantic. For comparison, a dust scavenging ratio of 241 nmol kg À1 water per nmol m À3 air for June-September was calculated here from sampling stations in South Florida (based on data presented in Prospero et al [2010]) and dust aerosol measurements at our coastal Miami site; the values from Florida appear to agree relatively well with the estimate of Duce et al (1991).…”

“…The deposition velocity of aerosol P was estimated at 0.01 m s À 1 AE a factor of 3 [Duce et al, 1991], as was that of NO 3 À , because it was found primarily in the coarse size fraction [Zamora et al, 2011]. As in Spokes et al [2000], we estimated ammonium deposition velocity at 0.006 m s À 1 AE a factor of 3 [Spokes et al, 2000].…”

“…V d is likely to be impacted not only by aerosol size and hygroscopicity but also by meteorological parameters such as rainfall, relative humidity, and wind speed [Prospero and Arimoto, 2009]. Thus, V d estimates are likely to have large associated errors, which are commonly assumed to be on the order of a factor of 3 based on various size-dependent processes [Duce et al, 1991]. Dry deposition estimates are presented in Table 8.…”

“…Thus, measured scavenging ratios were not accurate. Instead, the dust scavenging ratio of 200 nmol kg À1 water per nmol m À3 air from Duce et al [1991] was used for phosphorus. This ratio was based on measurements of dust in aerosols and rain over the North Atlantic.…”

Heavy metals in aerosols over the seas of the Russian Arctic

“…*Corresponding author. Numerous studies have shown that aerosols in the Arctic are important for atmospheric chemistry and climate (Rahn, 1981;Barrie, 1986Barrie, , 1996Pacyna, 1991;Leck et al, 1996;Sirois and Barrie, 1999;Bigg and Leck, 2001). There is much evidence that atmospheric inputs contribute significantly to the chemical budget of marine areas (Duce et al, 1991;Lisitzin, 1996), but in the Arctic their role is underestimated.…”