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Funding was provided through a NERC Research Training Support Grant awarded NE/L002590/1 to Ben Taylor and NERC grant NE/N011716/1 awarded to James Rae and Andrea Burke. Planktic foraminifera census data have been used to reconstruct past temperatures through transfer functions, as well as changes in ocean ecosystems, chemistry and circulation. Here we present new multinet, plankton net and core-top census data from 20 sites in the Subpolar North Pacific. We combine these with previous data to provide an up to date compilation of North Pacific planktic foraminifera assemblage data. Our compilation is used to define 6 faunal zones: the subpolar zone; transitional zone; upwelling zone; subtropical zone; east equatorial zone; west equatorial zone; based on the distribution of 10 major species of planktic foraminifera. Two species of planktic foraminifera Neogloboquadrina pachyderma and Globigerina bulloides provide the basis for many subpolar paleo-reconstructions. Through the analysis of new multinet and CTD data we find that G. bulloides and N. pachyderma are predominantly found within 0–50 m of the water column and coincide with high food availability. N. pachyderma also shows a strong temperature control and can thrive in food poor waters where temperatures are low. Both species bloom seasonally, particularly during the spring bloom of March to June, with G. bulloides exhibiting greater seasonal variation. We suggest that percentage abundance of N. pachyderma in paleo-assemblages can be used to assess relative changes in past temperature, with G. bulloides abundance more likely to reflect changes in food availability. By comparing our core-top and multinet data, we also find a dissolution bias of G. bulloides over N. pachyderma in the North Pacific, which may enrich assemblages in the latter species. Postprint

Coral skeletal growth is sensitive to environmental change and may be adversely impacted by an acidifying ocean. However, physiological processes can also buffer biomineralization from external conditions, providing apparent resilience to acidification in some species. These same physiological processes affect skeletal composition and can impact paleoenvironmental proxies. Understanding the mechanisms of coral calcification is thus crucial for predicting the vulnerability of different corals to ocean acidification and for accurately interpreting coral-based climate records. Here, using boron isotope ( δ 11 B ) measurements on cultured cold-water corals, we explain fundamental features of coral calcification and its sensitivity to environmental change. Boron isotopes are one of the most widely used proxies for past seawater pH, and we observe the expected sensitivity between δ 11 B and pH. Surprisingly, we also discover that coral δ 11 B is independently sensitive to seawater dissolved inorganic carbon (DIC). We can explain this new DIC effect if we introduce boric acid diffusion across cell membranes as a new flux within a geochemical model of biomineralization. This model independently predicts the sensitivity of the δ 11 B -pH proxy, without being trained to these data, even though calcifying fluid pH (pHCF) is constant. Boric acid diffusion can resolve why δ 11 B is a useful proxy across a range of calcifiers, including foraminifera, even when calcifying fluid pH differs from seawater. Our modeling shows that δ 11 B cannot be interpreted unequivocally as a direct tracer of pHCF. Constant pHCF implies similar calcification rates as seawater pH decreases, which can explain the resilience of some corals to ocean acidification. However, we show that this resilience has a hidden energetic cost such that calcification becomes less efficient in an acidifying ocean.

Funding was provided by an Antarctic Bursary awarded to J.A.S., ERC and NERC grants awarded to L.F.R. (278705, NE/S001743/1, NE/R005117/1) and L.F.R. and J.W.B.R. (NE/N003861/1), and a NERC Stable isotope Grant. The Li/Mg, Sr/Ca and oxygen isotopic (δ18O) compositions of many marine biogenic carbonates are sensitive to seawater temperature. Corals, as cosmopolitan marine taxa with carbonate skeletons that can be precisely dated, represent ideal hosts for these geochemical proxies. However, efforts to calibrate and refine temperature proxies in cold-water corals (

The middle Miocene Climatic Optimum (17-15Ma; MCO) is a period of global warmth and relatively high CO2 and is thought to be associated with a significant retreat of the Antarctic Ice Sheet (AIS). We present here a new planktic foraminiferal δ11B record from 16.6 to 11.8Ma from two deep ocean sites currently in equilibrium with the atmosphere with respect to CO2. These new data demonstrate that the evolution of global climate during the middle Miocene (as reflected by changes in the cyrosphere) was well correlated to variations in the concentration of atmospheric CO2. What is more, within our sampling resolution (~1 sample per 300kyr) there is no evidence of hysteresis in the response of ice volume to CO2 forcing during the middle Miocene, contrary to what is understood about the Antarctic Ice Sheet from ice sheet modelling studies. In agreement with previous data, we show that absolute levels of CO2 during the MCO were relatively modest (350-400ppm) and levels either side of the MCO are similar or lower than the pre-industrial (200-260ppm). These new data imply the presence of either a very dynamic AIS at relatively low CO2 during the middle Miocene or the advance and retreat of significant northern hemisphere ice. Recent drilling on the Antarctic margin and shore based studies indicate significant retreat and advance beyond the modern limits of the AIS did occur during the middle Miocene, but the complete loss of the AIS was unlikely. Consequently, it seems that ice volume and climate variations during the middle Miocene probably involved a more dynamic AIS than the modern but also some component of land-based ice in the northern hemisphere.

Accurate records of the state of the ocean carbonate system are critical for understanding past changes in pCO 2 , ocean acidification and climate. The chemical principles underlying the proxy of oceanic pH provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood, but the proxy's reliability has been questioned. We present 76 new Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICPMS) δ 11 B measurements on a range of benthic foraminifera from 23 late-Holocene samples from the Atlantic that reaffirm the utility of the δ 11 B-pH proxy. Our boron isotope measurements on ~ 10 benthic foraminifera tests typically yield a precision of ~ ± 0.25‰ at 2 s.d. (equivalent to ~ ± 0.03 pH units). δ 11 B values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of B(OH) 4 − from seawater and no vital effects, using the independently determined fractionation factor of 1.0272 between 11 B/ 10 B of aqueous boron species. Infaunal foraminifera are consistent with this model, but record the combined effects of lower pore-water δ 11 B and pH. No influence of partial dissolution or shell size on δ 11 B is observed. We have also measured the B/Ca ratios of the same samples. For individual Cibicidoides species, B/Ca shows a good correlation with Δ[CO 3 2− ], but the B/Ca of different co-occurring species morphotypes varies considerably. These effects are not seen in δ 11 B, which may therefore provide a more robust proxy of the ocean carbonate system. Whilst in theory δ 11 B and B/Ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate (DIC), in practice this is precluded by propagated uncertainties. δ 11 B data give significant constraints on foraminifera calcification mechanisms, and seem most simply explained by incorporation of B(OH) 4 − into a HCO 3 − pool, which is then completely incorporated in foraminiferal CaCO 3 . Our demonstration of the predictable variation of δ 11 B with pH, across a wide range of species and locations, provides confidence in the application of MC-ICPMS measurements of foraminiferal δ 11 B to reconstruct past changes in the ocean carbonate system.