time it grows to 1 cm in shell diameter 21 . Analysis was carried out on both freshly 90 caught material preserved directly upon collection and on specimens that were 91 incubated under manipulated CO 2 levels (375 to 750 parts per million at 4°C) in order 92 to establish a response index. All freshly-caught and incubated specimens were 93 preserved in 70% ethanol. Subsequently, they were treated to dehydrate shell-layers 94 and to remove the periostracum (Fig. 3) so that the state of the underlying shell matrix 95 could be examined using SEM. 96 97 Different degrees of dissolution were identified in incubated shells of live pteropods 98 (see supplementary information). We categorised them into three main levels 99 according to the degree of encroachment upon the upper prismatic layer and into the 100 upper shell layer (Fig. 4). Specimens were scored blind and then correlated back to 101 5 the experimental conditions. Incubations in which even only a slight degree of 102 undersaturation was experienced for 8 d (Ω A 0.94-1.12, pCO 2 of 675 µatm) was 103 sufficient to cause substantial dissolution of the shell matrix relative to the 104 supersaturated control (Ω A 1.62-1.78, Fig. 5). We then examined freshly caught 105 material, preserved directly upon collection, for signs of such shell dissolution. 106 107 L. helicina antarctica juveniles were found at all sampling stations, with northern 108 stations (<57ºS) containing higher abundances (7.2 x 10 4 to 3.4 x 10 4 ind. m -2 ) than 109 those to the south (>57ºS; 2.9 x 10 2 to 1.9 x 10 3 ind. m -2 ). At station Su9, we found L.

Anthropogenic ocean acidification is likely to have negative effects on marine calcifying organisms, such as shelled pteropods, by promoting dissolution of aragonite shells. Study of shell dissolution requires an accurate and sensitive method for assessing shell damage. Shell dissolution was induced through incubations in CO2‐enriched seawater for 4 and 14 days. We describe a procedure that allows the level of dissolution to be assessed and classified into three main types: Type I with partial dissolution of the prismatic layer; Type II with exposure of underlying crossed‐lamellar layer, and Type III, where crossed‐lamellar layer shows signs of dissolution. Levels of dissolution showed a good correspondence to the incubation conditions, with the most severe damage found in specimens held for 14 days in undersaturated condition (Ω ~ 0.8). This methodology enables the response of small pelagic calcifiers to acidified conditions to be detected at an early stage, thus making pteropods a valuable bioindicator of future ocean acidification.

[1] The deposition of ozone to seawater is known to be controlled by a variety of physical and chemical processes. At low wind speeds chemical loss is comparatively more important than loss due to physical processes. We have determined experimentally the relationship between ozone deposition velocity and concentration of iodide and dissolved organic matter in water buffered at seawater pH (8.0). The concentrations of both species used in this study are representative of those encountered in coastal and oceanic systems. We show that dissolved organic matter and iodide contribute to a similar degree to the chemical enhancement of ozone deposition to surface waters. Citation: Martino, M., B. Lézé, A. R. Baker, and P. S. Liss (2012), Chemical controls on ozone deposition to water, Geophys. Res. Lett., 39, L05809,

11Whilst the processes involved in the cycling of dissolved phosphorus (P) in rivers have been 12 extensively studied, less is known about the mechanisms controlling particulate P concentrations 13 during small and large flows. This deficiency is addressed through an analysis of large numbers of 14 suspended particulate matter (SPM) samples collected under baseflow (n = 222) and storm event (n = 15 721) conditions over a 23-month period across three agricultural headwater catchments of the River 16 Wensum, UK. Relationships between clay mineral and metal oxyhydroxide associated elements were 17 assessed and multiple linear regression models for the prediction of SPM P concentration under 18 baseflow and storm event conditions were formulated. These models, which explained 71-96% of the 19 variation in SPM P concentration, revealed a pronounced shift in P association from iron (Fe) 20 dominated during baseflow conditions to particulate organic carbon (POC) dominated during storm 21 events. It is hypothesised this pronounced transition in P control mechanism, which is consistent 22 across the three study catchments, is driven by changes in SPM source area under differing 23 hydrological conditions. In particular, changes in SPM Fe-P ratios between small and large flows 24 suggest there are three distinct sources of SPM Fe -surface soils, subsurface sediments and 25 streambed iron sulphide. Further examination of weekly baseflow data also revealed seasonality in the 26Fe-P and aluminium oxalate-dithionate (Al ox-Aldi) ratios of SPM, indicating temporal variability in 27 2 sediment P sorption capacity. The results presented here significantly enhance our understanding of 28 SPM P associations with soil derived organic and inorganic fractions under different flow regimes and 29 has implications for the mitigation of P originating from different sources in agricultural catchments. 30