Ocean–Atmosphere Interactions of Particles

Abstract

This chapter provides an overview of the current knowledge on aerosols in the marine atmosphere and the effects of aerosols on climate and on processes in the oceanic surface layer. Aerosol particles in the marine atmosphere originate predominantly from direct production at the sea surface due to the interaction between wind and waves (sea spray aerosol, or SSA) and indirect production by gas to particle conversion. These aerosols are supplemented by aerosols produced over the continents, as well as aerosols emitted by volcanoes and ship traffic, a large part of it being deposited to the ocean surface by dry and wet deposition. The SSA sources, chemical composition and ensuing physical and optical effects, are discussed. An overview is presented of continental sources and their ageing and mixing processes during transport. The current status of our knowledge on effects of marine aerosols on the Earth radiative balance, both direct by their interaction with solar radiation and indirect through their effects on cloud properties, is discussed. The deposition on the ocean surface of some key species, such as nutrients, their bioavailability and how they impact biogeochemical cycles are shown and discussed through different time and space scales approaches.

Overview and preliminary results of the Surface Ocean Aerosol Production (SOAP) campaign

“…Breaking waves and associated bubble formation are a major source of primary marine aerosol (PMA), supplying most of the aerosol mass in the marine boundary layer (MBL) over the remote ocean (Andreae and Rosenfeld, 2008) and particularly in regions that experience high winds and breaking waves (de Leeuw et al, 2014). This is reflected in PMA contributing only ∼ 10-20 % of CCN number concentrations over the remote Pacific Ocean (Blot et al, 2013;) but up to 55 % over the Southern Ocean (McCoy et al, 2015).…”

“…It is well-established that biologically productive regions are characterized by elevated concentrations and emissions of a range of compounds that may influence aerosol production, composition and properties (Meskhidze and Nenes, 2010;Gantt and Meskhidze, 2013;de Leeuw et al, 2014). However, the oceanic influence on atmospheric composition is not only attributable to PMAs but also to secondary marine aerosols (SMAs) that are produced during gas-phase reactions of volatile organic compounds (VOCs).…”

Dust in the Ocean

“…This link has been mostly explored in iron-limited, highnutrient low-chlorophyll (HNLC) regions (i.e., Boyd et al, 2007) after John Martin formulated his "iron hypothesis" linking stimulation of new production and atmospheric CO 2 drawdown during the last glacial maximum to higher atmospheric dust iron inputs at that time. Although a number of in situ mesoscale experiments and microcosm and mesocosm approaches since the 1990s have improved our understanding of the actual role of dust input in ocean biogeochemistry, our knowledge of the impact of dust deposition on the biogeochemistry of different areas of the ocean is still fragmented (de Leeuw et al, 2014). Dust dissolution experiments have shown the potential of dust to release nutrients such as phosphorus (e.g., Ridame and Guieu, 2002) and iron (e.g., Baker and Croot, 2010).…”

Evolving research directions in Surface Ocean - Lower Atmosphere (SOLAS) science

“…However observations and model estimates of the contribution of sea salt aerosol to the total (natural and anthropogenic) global short-wave direct radiative effect and the global aerosol optical depth have large uncertainties, with values ranging from 18 to 50 %. [72] Furthermore sea salt source functions used in different global models and model estimations of sea salt dry mass vary by a factor of five. [62,63,73,74] Recent advances in understanding and quantification of emission and production mechanisms include the extension of the sea spray source function to particles with r 80 of ,10 nm, which is important for the assessment of aerosol effects on clouds.…”

“…5). Yet, despite significant experimental, field and modelling studies over the past decade, [72] the links between atmospheric deposition of nutrients, ocean productivity and feedbacks to climate are still poorly understood. Consequently, the role of atmospheric inputs remains under-represented in budgets and marine biogeochemical models (C. Guieu, O. Aumont, L. Bopp, C. Law, N. Mahowald, E. P. Achterberg, et al, unpubl.…”