[1] Remote sensing of Southern Ocean chlorophyll concentrations is the most effective way to detect large-scale changes in phytoplankton biomass driven by seasonality and climate change. However, the current algorithms for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, algorithm OC4v6), the Moderate Resolution Imaging Spectroradiometer (MODIS-Aqua, algorithm OC3M), and GlobColour significantly underestimate chlorophyll concentrations at high latitudes. Here, we use a long-term data set from the Southern Ocean (20 -160 E) to develop more accurate algorithms for all three of these products in southern high-latitude regions. These new algorithms improve in situ versus satellite chlorophyll coefficients of determination (r 2 ) from 0.27 to 0.46, 0.26 to 0.51, and 0.25 to 0.27, for OC4v6, OC3M, and GlobColour, respectively, while addressing the underestimation problem. This study also revealed that pigment composition, which reflects species composition and physiology, is key to understanding the reasons for satellite chlorophyll underestimation in this region. These significantly improved algorithms will permit more accurate estimates of standing stocks and more sensitive detection of spatial and temporal changes in those stocks, with consequences for derived products such as primary production and carbon cycling.

Quaternary volcanic rocks from the New Britain island arc display INTRODUCTION a wide range in chemical compositions. The source of the lavas The New Britain region of Papua New Guinea represents shares isotopic characteristics with Indian Ocean type mid-ocean an outstanding opportunity to reach an understanding ridge basalt (MORB). In contrast, the high field strength elements of the processes of magma genesis in an oceanic island (HFSE) are extremely depleted in the volcanic front rocks compared arc. The Quaternary volcanoes found there define the with MORB. We propose that this results from a previous melteastern part of the Bismarck volcanic arc, and have extraction event-hypotheses invoking residual phases in either the formed in response to northward subduction of the small mantle wedge or subducting slab cannot account for the depletion Solomon plate beneath the Bismarck plate (Fig. 1). The relative to MORB. In addition, elements other than the HFSE are New Britain arc is outstanding for two main reasons: also affected. Chemical signatures in parts of the New Britain arc(1) Arc volcanism in the central sector of the island and Manus Basin may relate to a previous subduction episode has taken place over an exceptionally wide range of along the now inactive Vitiaz-West Melanesian trench. Ultradepths to the Wadati-Benioff zone-from~100 km deep depleted volcanic front basalts invariably have strong 'fluid'-related at the 'volcanic front' (closest to the submarine trench) trace element signatures, including high Sr/Nd and U/Th (and down to~600 km in the northwest beneath the Witu 238 U disequilibrium), together with positive Eu anomalies that can Islands. The reasons for the correspondingly large width be related to the mobility of Eu 2+ in the slab-derived flux. Negative of the volcanic arc are still unknown, but isotopic and Ce anomalies are attributed to a minor sedimentary component. elemental differences between the rocks are systematic Across-arc geochemical profiles record a decrease in the degree of as depths to the Wadati-Benioff zone increase. We believe partial melting and diminishing influence of a slab-derived fluid that these differences provide unparalleled insights into with depth, superimposed upon the depleted mantle composition the geochemical architecture of subduction-zone systems. beneath the volcanic front. Element partitioning into (and not(2) Rocks of the New Britain volcanic front are low in necessarily the source of) the fluid is considered to exert strong control potassium, range from basalt to rhyolite, and have (as on the chemistry of volcanic front magmas, a feature that may go illustrated below) exceptional depletions in high field some way to explaining the contradictory estimates of the slab flux strength elements (HFSE). Indeed, they may represent derived from isotope vs trace element data in many subduction suites. the most HFSE-depleted arc rocks known. These rocks therefore should provide valuable constraints on the controls of HFSE abundances in island-arc magmas. The depl...

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Abstract. Aerosol observations above the Southern Ocean and Antarctic sea ice are scarce. Measurements of aerosols and atmospheric composition were made in East Antarctic pack ice on board the Australian icebreaker Aurora Australis during the spring of 2012. One particle formation event was observed during the 32 days of observations. This event occurred on the only day to exhibit extended periods of global irradiance in excess of 600 W m −2 . Within the single air mass influencing the measurements, number concentrations of particles larger than 3 nm (CN 3 ) reached almost 7700 cm −3 within a few hours of clouds clearing, and grew at rates of 5.6 nm h −1 . Formation rates of 3 nm particles were in the range of those measured at other Antarctic locations at 0.2-1.1 ± 0.1 cm −3 s −1 . Our investigations into the nucleation chemistry found that there were insufficient precursor concentrations for known halogen or organic chemistry to explain the nucleation event. Modelling studies utilising known sulfuric acid nucleation schemes could not simultaneously reproduce both particle formation or growth rates. Surprising correlations with total gaseous mercury (TGM) were found that, together with other data, suggest a mercurydriven photochemical nucleation mechanism may be responsible for aerosol nucleation. Given the very low vapour pressures of the mercury species involved, this nucleation chemistry is likely only possible where pre-existing aerosol concentrations are low and both TGM concentrations and solar radiation levels are relatively high (∼ 1.5 ng m −3 and ≥ 600 W m −2 , respectively), such as those observed in the Antarctic sea ice boundary layer in this study or in the global free troposphere, particularly in the Northern Hemisphere.

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