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Culture experiments were carried out with the species Orbulina universa at four different pH values (7.70±0.05, 8.15±0.05, 8.60±0.05, and 9.00±0.10) in order to establish the pH‐dependence of boron isotope fractionation between seawater and foraminifera. A clear relationship between the boron isotopic composition of the foraminifera and the pH of the seawater culture solutions was found, showing heavier boron isotopic composition at higher pH. This finding supports the viability of boron isotopes as a paleo‐pH tool. It is important to note that Orbulina universa cultured in natural seawater, as well as those obtained from coretop samples, have a significantly lighter boron isotopic ratio than Globigerinoides sacculifer from coretop samples, suggesting that at least for this species, a vital effect is active.

Abstract-Experiments involving boron co-precipitation with calcite have been carried out inorganically under controlled pH conditions (7.9 Ϯ 0.05, 8.3 Ϯ 0.05 and 8.6 Ϯ 0.05) to determine the dependence of the boron isotopic composition (␦ 11 B) of calcite on the pH of seawater. Another purpose of these experiments was to estimate the magnitude of the biogenic influence on the ␦ 11 B value of foraminifera by comparing their boron isotopic composition with that of the inorganic calcite over a common pH range. The results show a clear relationship between ␦ 11 B of inorganic calcite and the pH of artificial seawater. The variation of boron isotopic fractionation between seawater and calcite with pH, estimated from these experiments, is similar to that estimated for cultured O. universa and the theoretically predicted trend. The results also support the hypothesis that B(OH) 4 Ϫ is the dominant species incorporated into the calcite structure. However, the boron isotopic fractionation between seawater and inorganic calcite is lower than that estimated for O. universa indicating the presence of a biogenic effect on the boron isotopic composition at least of this species of foraminifera. Most importantly, the results imply that in spite of a small biogenic influence on the boron isotopic composition of foraminifera, the variation in ␦ 11 B of foraminiferal shells with pH (at least for O. universa) is comparable to that for inorganic calcite, supporting the potential of this isotopic signature in foraminifera as a reliable paleo pH proxy.

Abstract. Culture experiments were carried out with the planktonic foraminifera Globigerinoides sacculifer at three different pH values (7.6+0.05, 8.20+0.05, and 8.60+0.05) in order to establish the pH dependence of the boron isotopic fractionation between the calcitic tests of G. sacculifer and seawater. Additional objectives were to compare the pH dependences of boron isotopic composition of G. sacculifer with that of Orbulina universa and inorganic calcite in order to evaluate the robustness of the boron isotope paleo-pH proxy. The relationship between the boron isotopic composition of G. sacculifer and the culture water pH shows heavier boron isotopic values at higher pH. This empirical relationship is similar but offset (by-3%0) from that of O. universa, indicating the presence of biogenic influence ("vital effect") on the boron isotopic composition of foraminifera. However, comparison of the boron isotopic composition of O. universa and G. sacculifer with that of inorganic calcite grown over a common pH range shows that inorganic processes are the dominant control on the boron isotopic composition of foraminifera and the "vital effects" play a small but not insignificant role. The results imply that in spite of a small biogenic influence the variation in boron isotopic composition of foraminiferal shells with pH (at least for O. universa and G. sacculifer) is consistent with that for inorganic calcite, demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo pH proxy.

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Abstract. Estimates of paleo-pH for the eastern equatorial Pacific Ocean across the oxygen isotopic stage 5-6 boundary have been made based on the boron isotopic composition of planktonic (Orbulina universa) and benthic (mixed species) foraminifera from core V19-28. The estimated deep ocean pH during the penultimate glacial period was about 0.3+0.1 pH units higher compared to the modern deep ocean. This is consistent with previously estimated deep ocean pH changes across the stagel-2 boundary in the western equatorial Pacific and tropical Atlantic, thus arguing against the possibility that the benthic foraminifera analyzed to estimate deep ocean pH changes have been significantly affected by anomalous local environment and/or diagenesis. The estimated changes in the deep ocean carbonate chemistry require a alecoupling (of several kilometers) between the saturation horizon and the lysocline during the glacial periods. Though such a decoupling could be achieved by enhanced respiration CO2 driven calcite dissolution in sediments during glacial periods, it lacks support from the calcite sedimentary records. The boron isotopic compositions of planktonic foraminifera, on the other hand, indicate no significant pH change in the eastern equatorial Pacific surface ocean during the glacial-interglacial transition. This is inconsistent with an expected higher surface ocean pH during the glacial period due to lower atmospheric pCO2 and is also in contrast with the previously estimated boron isotope based glacial-interglacial pH change of 0.2_-+0.1 pH units in the western equatorial Pacific and tropical Atlantic. The lack of change in eastern equatorial Pacific surface ocean pH between glacialinterglacial periods could be attributed to less nutrient utilization efficiency and/or enhanced calcite production during glacial periods. Such a decrease in nutrient utilization efficiency and/or increase in calcite production would lead to a greater disequilibrium between the pCO2 of eastern equatorial Pacific surface ocean and that of the amaosphere, making this pan of the ocean a greater source of CO2 to the atmosphere during glacial periods compared to today.

whitings are dominated by re-suspended sediment. We offer a new and highly speculative mechanism for this re-suspension. Black-tipped sharks which inhabit whitings purposefully stir up the sediment in order to create a trap for fish, much as spiders construct webs as traps for insect prey.