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The isotopic composition of dissolved oxygen offers a family of potentially unique tracers of respiration and transport in the subsurface ocean. Uncertainties in transport parameters and isotopic fractionation factors, however, have limited the strength of the constraints offered by¹⁸O/¹⁶O and¹⁷O/¹⁶O ratios in dissolved oxygen. To improve our understanding of oxygen cycling in the ocean's interior, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2‐D isotopologue‐enabled isopycnal reaction‐transport model. We measured¹⁸O/¹⁶O and¹⁷O/¹⁶O ratios, as well as the “clumped”¹⁸O¹⁸O isotopologue in the northeast Pacific, and compared the results to previously published data. We find evidence that oxygen consumption in the northeast Pacific follows different mass‐dependent fractionation exponents from those typically used in oceanographic studies. These fractionation factors imply that an elevated proportion of¹⁷O compared to¹⁸O in dissolved oxygen—that is, its triple‐oxygen isotope composition—may not uniquely reflect only gross primary productivity and mixing. For all oxygen isotopologues, transport, respiration, and photosynthesis comprise important parts of their respective budgets. Mechanisms of oxygen removal in the subsurface ocean are discussed.

The cycling of biologically produced calcium carbonate (CaCO₃) in the ocean is a fundamental component of the global carbon cycle. Here, we present experimental determinations of in situ coccolith and foraminiferal calcite dissolution rates. We combine these rates with solid phase fluxes, dissolved tracers, and historical data to constrain the alkalinity cycle in the shallow North Pacific Ocean. The in situ dissolution rates of coccolithophores demonstrate a nonlinear dependence on saturation state. Dissolution rates of all three major calcifying groups (coccoliths, foraminifera, and aragonitic pteropods) are too slow to explain the patterns of both CaCO₃sinking flux and alkalinity regeneration in the North Pacific. Using a combination of dissolved and solid‐phase tracers, we document a significant dissolution signal in seawater supersaturated for calcite. Driving CaCO₃dissolution with a combination of ambient saturation state and oxygen consumption simultaneously explains solid‐phase CaCO₃flux profiles and patterns of alkalinity regeneration across the entire N. Pacific basin. We do not need to invoke the presence of carbonate phases with higher solubilities. Instead, biomineralization and metabolic processes intimately associate the acid (CO₂) and the base (CaCO₃) in the same particles, driving the coupled shallow remineralization of organic carbon and CaCO₃. The linkage of these processes likely occurs through a combination of dissolution due to zooplankton grazing and microbial aerobic respiration within degrading particle aggregates. The coupling of these cycles acts as a major filter on the export of both organic and inorganic carbon to the deep ocean.