Climate change is currently driving the expansion of oxygen minimum zones (OMZs), areas of the open ocean with consistently low oxygen levels. Changes in temperature, productivity and consequent respiration, and water mass ventilation drive OMZ expansion and contraction with implications for ecosystem function and biogeochemical cycling. However, there is uncertainty in how OMZs respond to climatic change on longer timescales. The structure and drivers of OMZ change in the Eastern Tropical North Pacific (ETNP) are investigated through the most recent period of rapid warming (similar to 20.7-10 ka) using planktic foraminiferal assemblages, radiocarbon ventilation ages, foraminiferal delta 18O, delta 13C, I/Ca records, and bulk sediment delta 15N. Evidence from core MAZ-1E-04 (22 degrees 54.29 ' N, 106 degrees 54.59 ' W; 1,463 m depth) from the Mexican Margin shows the OMZ intensified during the mid-deglaciation relative to the Last Glacial Maximum (LGM) with potential shifts in bottom water ventilation. Oxygen isotopes from planktic foraminifera at multiple depth habitats, including OMZ dweller Globorotaloides hexagonus, indicate shallowing of the OMZ similar to 14 ka with continued expansion near the thermocline through the mid-deglaciation. No systematic shifts in productivity are captured by the records, suggesting ventilation as the primary driver of OMZ restructuring at this site. Radiocarbon ventilation ages provide evidence for a potential decoupling of intermediate and shallower waters with a boundary similar to 1-1.5 km; however, open questions about radiocarbon ventilation ages near Baja California warrant a careful interpretation of this record.

Proxy records of seawater radiocarbon (14C/C) provide strong constraints on how changes in ocean ventilation contributed to the increase in atmospheric CO2 during the termination of the last ice age (approximate to 18,000-to-12,000 years ago). One outstanding problem, however, is the existence of anomalously low deglacial benthic foraminiferal 14C/C in the intermediate-depth Eastern Tropical North Pacific (ETNP) near the Gulf of California (GoC). This deglacial ETNP 14C/C anomaly is hypothesized to reflect either (a) an artifact of the proxy record, (b) the advection of low 14C/C seawater, or (c) the input of 14C/C-depleted geologic carbon related to local seafloor volcanism. To test these hypotheses, we first use new sediment-trap and seaweed 14C/C to establish a new baseline understanding of ETNP seawater 14C/C, which suggest that anomalously low 14C/C is upwelled in the modern GoC. We then apply new geochemical experiments to test and ultimately validate the utility of the benthic foraminiferal 14C/C as a proxy for seawater 14C/C. Finally, we present a compilation of published and new glacial-interglacial benthic foraminiferal 14C/C records, specifically developed to map the spatial and temporal variability of the intermediate-depth water mass containing the deglacial ETNP 14C/C anomaly. These results clearly show that the ETNP deglacial 14C/C anomaly develops near the GoC mouth, concomitant with local hydrothermal systems. Considering these results and those of our companion paper (Green et al., 2026, https://doi.org/10.1029/2025pa005217), we argue that the input of pH-neutral geologic carbon from hydrothermal vents near and within the GoC could explain the anomalous intermediate-depth 14C/C values both during the deglaciation and today.

The rapid response of foraminiferal assemblages to changing climate makes their shells an invaluable geological record of the past. However, the time frame over which foraminifera respond to climatic signals and the specific drivers influencing assemblage composition and abundance remain obscure. We focus on the impact of ongoing, anthropogenic climate change on planktic foraminifera in the California Current ecosystem, which would appear as a nearly instantaneous event in the sediment record. The Santa Barbara Basin sediment trap, located off the coast of California, USA since 1993, provides a record of more than 30 years of particulate and foraminiferal flux in the basin. The sediment trap captures the superposition of the annual cycle of seasonal upwelling, Pacific multiannual El Ni & ntilde;o-Southern Oscillation-driven temperature changes, and anthropogenically forced climate change. We present data on planktic foraminiferal flux collected between 2014-2021, at two-week intervals (164 samples, 60 006 individuals) and compare results to previously published data from 1993-1998. Consistent with previous studies, the most abundant species from 2014-2021 were Globigerina bulloides, Neogloboquadrina incompta, and Turborotalita quinqueloba, with peak fluxes occurring in the spring and summer. Lower fluxes and an increase in the abundance of N. incompta and subtropical species characterize the winter season. We find a 37.9 % decrease in total foraminiferal flux relative to the 1990s, primarily driven by a decrease in G. bulloides abundance. This decrease is accompanied by a 21.0 % overall reduction in calcium carbonate flux. We also find a decrease in the relative abundance of subtropical species (Globigerinoides ruber, Orbulina universa, and Neogloboquadrina dutertrei) and their fluxes compared to the 1990s, opposite expectations if assemblages and fluxes were to follow anthropogenic warming signals. We hypothesize that the observed decrease in subtropical species abundance and flux is likely related to an increase in acidification and in the timing and magnitude of upwelling along the California coast. The extremely rapid responses of foraminifera to ongoing changes in carbonate chemistry and temperature suggest that climate change is already having a meaningful impact on coastal carbon cycling. The observed decrease in particulate inorganic carbon (PIC) flux relative to particulate organic carbon (POC) flux may facilitate increased oceanic uptake of atmospheric CO2.

The vast majority of planktic foraminiferal culture studies have been carried out on spinose species of foraminifera, with relatively few studies on non-spinose species. We conducted a pilot study to test whether live specimens of the non-spinose planktic foraminifera, Globorotalia truncatulinoides and Globorotalia menardii, could be successfully harvested from offshore plankton tow samples in the Gulf of America (Gulf of Mexico) and kept alive in a laboratory at the US Geological Survey St. Petersburg Coastal and Marine Science Center. We collected several G. truncatulinoides specimens (n = 39) from the surface mixed-layer (0-80 meters) via vertical plankton tow in February 2020 during a sediment trap mooring recovery cruise. We collected G. menardii (n = 27) from the upper 200 meters of the water column on follow-up cruises in December 2021 and November 2022. The G. truncatulinoides specimens stayed alive in the laboratory for 8-76 days, and G. menardii for 7-29 days. All non-spinose foraminifera in this study showed a strong preference for eating marine snow aggregates from the plankton tow over Artemia nauplii. Using a combination of morphometric observations and geochemical analysis of the foraminiferal tests, we demonstrate that some specimens of both species grew new chambers while in culture, whereas other individuals added a calcite crust to the final whorl. The G. menardii were cultured in 87Sr-labeled seawater, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to verify the presence of laboratory grown calcite. Our results shed light on the feeding behavior and growth patterns in these two upper-ocean species of non-spinose foraminifera. This study demonstrates the feasibility of conducting laboratory culture experiments with G. truncatulinoides and G. menardii collected via plankton tow in the open ocean.

This study presents a high-resolution record of δ15Nsed, which serves as a proxy for water column denitrification and oxygen minimum zone (OMZ) intensity, from the Soledad Basin in the Eastern Tropical North Pacific OMZ. The Soledad Basin δ15Nsed record is compared to the Pescadero Slope and Santa Barbara Basin (SBB) δ15Nsed records to gain insight into regional variations in the ETNP OMZ. During the Medieval Climate Anomaly (MCA; 950–1250 CE), Soledad Basin, Pescadero Slope, and SBB records exhibit coherent trends suggesting that there was general water column oxygenation stability. During the Little Ice Age (LIA; 1350–1850 CE), Soledad Basin and SBB showed a similar decreasing trend in δ15Nsed values while the Pescadero Slope δ15Nsed exhibited an increasing trend until values abruptly declined between 1740 and 1840 CE. We suggest that increased δ15Nsed variability and the different trends at the Pescadero Slope during the LIA are due to the influence of the North American monsoon (NAM), which can suppress upwelling when enhanced and result in OMZ contraction. The decoupling between the Soledad Basin, SBB, and the Pescadero Slope could also be due to the increased influence of enriched 15NO3− subarctic waters in the California Current System. Since each site is influenced by local productivity, basin morphology, and regional atmospheric and ocean circulation patterns, we suggest that assessing OMZ fluctuations from multiple sites provides a more comprehensive view of regional OMZ dynamics in response to climate variations.

The impacts of El Niño 2015–2016 on planktonic foraminiferal assemblages and particle fluxes (total mass, organic carbon, total nitrogen, and carbonate) were analyzed in a sediment trap record located at the entrance of the Gulf of California from 2015 to 2019. Biweekly data of the sea surface temperature (SST) and sea surface chlorophyll-a (Chl-a) were obtained from satellite images (MODIS-AQUA) during this period. Particle fluxes and planktonic foraminiferal assemblages reflected the seasonal cycles of SST and phytoplankton biomass highlighting the effects of El Niño 2015–2016. During neutral and La Niña conditions, winter-spring upwelling leads to low SST, high Chl-a and particle fluxes, and an assemblage dominated by Globigerina bulloides while the summers are characterized by high SST, low Chl-a and particle fluxes, and a Globorotaloides hexagonus assemblage. In contrast, in normal summers, there is an alternation of G. bulloides and Orbulina universa-Trilobatus sacculifer-Globigerinella siphonifera associations. By late autumn under La Niña conditions, the Globigerinita glutinata assemblage reflects the transition from warm to cold conditions and the beginning of the upwelling season. This general pattern was affected by El Niño during 2015–2016. From late summer 2015 to early winter 2016 (El Niño 2015–2016 maximum intensity), Globigerinoides tenellus dominated, reflecting the intrusion of warm and oligotrophic equatorial waters. These results show the strong influence of El Niño Southern Oscillation (ENSO) on oceanic dynamics and planktonic foraminiferal assemblages at the entrance of the Gulf of California, and allow for a better interpretation of the preservation of these anomalous warm events in the sedimentary record, which can provide a better understanding of the long-term variations and effects of ENSO.

Abstract Upper-plate and lower-plate asymmetric passive margin fragments are preserved within Carolinia, one of several terranes that rifted from Gondwana in the Furongian (late Cambrian) to form the Rheic Ocean. In the upper plate, 1–2 km of preserved rocks are middle Cambrian (Drumian, Ptychagnostus atavus zone) trilobite-bearing mudstones that lie above an angular unconformity and are the youngest stratified rocks in Carolinia. In the lower plate, 4–5 km of stratigraphy preserved in the Kings Mountain terrane are particularly interesting, because a 4 km thick Cambrian Series 2 clastic sedimentary section increasingly dominated by western Amazonian detritus lies above a Carolinian volcanic arc basement. Here, we describe for the first time the origin and setting of the youngest rocks in the Appalachians of wholly Gondwanan origin.

Las particulas en el mar tienen un origen organico o inorganico, y sedimentan hacia aguas profundas y el fondo; factor que mantiene la vida en el oceano sin luz y proceso que secuestra carbono de la hidrosfera y atmosfera. En la Fosa de Cariaco, sitio de alta productividad biologica y aguas profundas anoxicas, se mantuvo un sistema de trampas de sedimentos durante 20 anos. Se actualizan los resultados del flujo de particulas entre 225 a 1210 m de profundidad, midiendo componentes basicos como el carbono organico (Corg), nitrogeno (N), opalo (silice biogenica), carbonato calcico (CaCO3) y terrigenos (fraccion de origen litogenico). El flujo estuvo relacionado con las condiciones climaticas e hidrograficas. La variabilidad fue notable, tanto estacional como a largo plazo. Aunque el flujo total no presento tendencias signiticativas, las proporciones de los componentes Corg, N y opalo disminuyeron, y los de CaCO3 y los terrigenos aumentaron, reflejando cambios en la composicion del fitoplancton, fuente principal de la materia organica. Hubo en general una correlacion positiva del flujo de Corg, N y opalo con la produccion primaria y la clorofila, aunque en la epoca de surgencia no se registro correlacion debido a una mayor tasa de reciclado de la materia organica. El zooplancton tuvo influencia en el transporte hacia aguas profundas anoxicas. Cerca del fondo en Cariaco llega un flujo de materia en particulas de 9,32 ± 5,47 g m-2 mes-1, del cual 0,82 ± 0,35 g m-2 mes-1 es Corg, un 2,37% ± 1 % del C fijado en superficie. Particle flux in the Cariaco Basin, results of two decades of observations 1995 – 2016 Abstract: The particles in the sea have an organic or inorganic origin, and sediment towards deep waters and the bottom; factor that maintains life in the dark ocean and process that sequesters C from the hydrosphere and atmosphere. In the Cariaco Basin site with high biological productivity and deep anoxic waters, an array of sediment traps was maintained for 20 years. The results of the particle flux between 225 to 1210 m depth were updated, measuring the basic components, organic C, N, opal (biogenic silica), carbonates (CaCO3) and terrigenous (fraction of lithogenic origin). The flux was related to the climatic and hydrographic conditions. The variations were notable, both seasonal and long-term. Although the total flux did not show significant trends in the time series, the proportions of the organic carbon (Corg,), nitrogen (N) and opal components decreased over time, while calcium carbonate (CaCO3) and terrigenous materials increased, reflecting changes in the composition of phytoplankton as the bulk origin of organic matter. There was a general positive correlation of Corg, N, and opal flux with primary production and chlorophyll at the surface, although in the upwelling season there was no correlation due to a higher recycling rate of organic matter. Zooplankton had influence on transport to anoxic deep water. Near the bottom in Cariaco comes a flux of particulate matter of 9.32 ± 5.47 g m-2 month-1 of which 0.82 ± 0.35 g m-2 month-1 is Corg, which represents 2.37% ± 1% of the C fixed on the surface.

Climate conditions and instantaneous depositional events can influence the relative contribution of sediments from terrestrial and marine environments and ultimately the quantity and composition of carbon buried in the sediment record. Here, we analyze the elemental, isotopic, and organic geochemical composition of marine sediments to identify terrestrial and marine sources in sediment horizons associated with droughts, turbidites, and floods in the Santa Barbara Basin (SBB), California, during the last 2,000 years. Stable isotopes (δ13C and δ15N) indicate that more terrestrial organic carbon (OC) was deposited during floods relative to background sediment, while bulk C to nitrogen (C/N) ratios remained relatively constant (~10). Long‐chain n‐alkanes (C27, C29, C31, and C33), characteristic of terrestrial OC, dominated all types of sediment deposition but were 4 times more abundant in flood layers. Marine algae (C15, C17, and C19) and macrophytes (C21 and C23) were also 2 times higher in flood versus background sediments. Turbidites contained twice the terrestrial n‐alkanes relative to background sediment. Conversely, drought intervals were only distinguishable from background sediment by their higher proportion of marine algal n‐alkanes. Combined, our data indicate that 15% of the total OC buried in SBB over the past 2,000 years was deposited during 11 flood events where the sediment was mostly terrestrially derived, and another 12% of deep sediment OC burial was derived from shelf remobilization during six turbidite events. Relative to twentieth century river runoff, our data suggest that floods result in considerable terrestrial OC burial on the continental margins of California.

The ratio of boron to calcium (B/Ca) in a subset of foraminifera has been shown to covary with seawater carbonate chemistry, making this geochemical signature a promising proxy for carbon cycle science. Some studies suggest complications with the B/Ca proxy in photosymbiont-bearing planktonic foraminifera, while relatively few studies have investigated B/Ca in species that lack large dinoflagellate symbionts. For the first time, we use a sediment trap time series to evaluate B/Ca of subtropical and subpolar planktonic foraminifera species that are asymbiotic (Globigerina bulloides and Neogloboquadrina incompta) and a species that hosts small intrashell photosymbionts (Neogloboquadrina dutertrei). We find that B/Ca measurements across size fractions indicate overall little to no size-dependent uptake of boron that has previously been reported in some symbiont-bearing foraminifera. Neogloboquadrina incompta and N. dutertrei B/Ca are strongly correlated with calcite saturation, pH, and carbonate ion concentration, which is in good agreement with the limited number of published core top results. While G. bulloides B/Ca trends with seasonal fluctuations in carbonate chemistry, during discrete periods considerable B/Ca offsets occur when a cryptic G. bulloides species is known to be seasonally present within the region. We confirm presence and significant B/Ca offset between cryptic species by individual LA-ICP-MS analyses. This finding calls into question the use of traditional morphological classification to lump what might be genetically distinct species for geochemical analyses. Our overall results highlight the utility of G. bulloides, N. incompta, and N. dutertrei B/Ca while bringing to light new considerations regarding divergent geochemistry of cryptic species.

Key Points Introduction to special issue

Seasonal and interannual variability in dinoflagellate cyst production were assessed using a 12.5 year-long sediment trap time series from the Cariaco Basin (southern Caribbean Sea). This study constitutes the longest such time series published to date, providing robust patterns of variability for individual dinoflagellate cyst taxa as well as for major phytoplanktonic and (micro-)zooplanktonic groups at the site. Cyst production is interpreted in the context of physico-chemical properties measured in situ at the mooring site (primarily reflecting seasonal upwelling), and considering potential interactions with other major components of the pelagic food web (e.g., diatoms, ciliates, copepods). The time series consists in > 300 sediment trap samples, each representing similar to 14 days of sedimentation, collected at the CARIACO station between Nov. 8, 1996 and May 19, 2009. Mass fluxes of biogenic silica, calcium carbonate and organic carbon reflect dominantly the timing and strength of wind-driven, seasonal upwelling that brings colder, nutrient-rich waters to the surface, fostering primary productivity and the export of biogenous materials to the depths. On seasonal time scales, dinoflagellate cyst production is closely coupled with upwelling strength, with higher cyst fluxes consistently observed under active upwelling conditions (average of 50.5 x 10(3) cysts m(-2) day(-1)) compared to non-active upwelling intervals (29.0 x 10(3) cysts m(-2) day(-1)). Yearto-year variability is characterized by a large increase in cyst production observed over the last similar to 4 years of the time series (2006-2009) and minimum cyst fluxes recorded in the years 1998 and 1999, following the strong 1997/98 El Nino event. Dinoflagellate cyst assemblages are dominated by Brigantedinium spp. (59.1%), accompanied by Echinidinium delicatum (10.8%), Bitectatodinium spongium (8.4%), Spiny brown type A (2.9%) and Echinidinium spp. (2.4%). Cyst produced by both autotrophic and heterotrophic dinoflagellates generally respond positively to upwelling in the basin. Most cyst taxa are associated with active upwelling conditions (e.g., Bitectatodinium spongium, Brigantedinium spp., Echinidinium delicatum, Quinquecuspis concreta, Selenopemphix quanta, Spiny brown type C), with some showing higher fluxes under active but weak upwelling conditions (e.g., Echinidinium granulatum, Echinidinium spp., cyst of P. fukuyoi, Spiny brown type A). Other cyst taxa tend to show higher abundances at the onset of upwelling conditions (e.g., Echinidintum aculeatum, cyst of Protoperidinium steam) or following active upwelling intervals (e.g., Lejeunecysta marieae, Selenopemphix nephroides). The detailed response of each dinoflagellate cyst taxon to environmental variability is presented in the form of an atlas, providing photo-micrographs and detailing overall monthly production, contribution to the total trap assemblage as well as cyst production over the 12.5 years of the time series.

The CARIACO (Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.50°N, 64.66°W, observed biogeochemical and ecological processes in the Cariaco Basin of the southwestern Caribbean Sea from November 1995 to January 2017. The program completed 232 monthly core cruises, 40 sediment trap deployment cruises, and 40 microbiogeochemical process cruises. Upwelling along the southern Caribbean Sea occurs from approximately November to August. High biological productivity (320-628 g C m-2 y-1) leads to large vertical fluxes of particulate organic matter, but only approximately 9-10 g C m-2 y-1 fall to the bottom sediments (∼1-3% of primary production). A diverse community of heterotrophic and chemoautotrophic microorganisms, viruses, and protozoa thrives within the oxic-anoxic interface. A decrease in upwelling intensity from approximately 2003 to 2013 and the simultaneous overfishing of sardines in the region led to diminished phytoplankton bloom intensities, increased phytoplankton diversity, and increased zooplankton densities. The deepest waters of the Cariaco Basin exhibited long-term positive trends in temperature, salinity, hydrogen sulfide, ammonia, phosphate, methane, and silica. Earthquakes and coastal flooding also resulted in the delivery of sediment to the seafloor. The program's legacy includes climate-quality data from suboxic and anoxic habitats and lasting relationships between international researchers.

Oxygen minimum zones (OMZs) are predicted to expand in the near future due to continued global warming, with largest declines in oxygen occurring within the strong tropical OMZs. In this study, shifts in the position and intensity of the OMZ in the Eastern Tropical North Pacific (ETNP) were examined using three 210Pb-dated sediment cores collected along the continental shelf and slope of the NW Mexican Margin (southwest of Mazatlán). Using a suite of redox sensitive elements, bulk element and physical analyses, three main factors were identified as driving the geochemical signatures of trace elements across the NW Mexican Margin: 1) terrigenous input, 2) organic matter scavenging and 3) bottom water oxygen content. Downcore trends in benthic foraminiferal assemblages and authigenic concentrations of Mo and U suggest that dysoxic conditions were more intense and covered a larger depth range prior to the 20th century followed by a reduction in both size and strength of the OMZ over the last century.

Decades of observations show that the world's oceans have been losing oxygen, with far-reaching consequences for ecosystems and biogeochemical cycling. To reconstruct oxygenation beyond the limited scope of instrumental records, proxy records are needed, such as sedimentary delta N-15. We combine two delta N-15 records from the Santa Barbara Basin (SBB), a 24-year-long, biweekly sediment trap time series, and a 114-year, high-resolution sediment core together spanning the years 1892-2017. These records allow for the examination of delta N-15 variability on seasonal to centennial timescales. Seasonal variability in SBB delta N-15 is consistent in timing with the poleward advection of a high delta N-15 signal from the Eastern Tropical North Pacific in the summer and fall. Strong El Nino events result in variable delta N-15 signatures, reflective of local rainfall, and neither the Pacific Decadal Oscillation nor North Pacific Gyre Oscillation impose strong controls on bulk sedimentary delta N-15. Seasonal and interannual variability in sediment trap delta C-13(org) is consistent with local productivity as a driver; however, this signal is not retained in the sediment core. The time series from the sediment trap and core show that bulk sedimentary delta N-15 in SBB has now exceeded that measured for the past 2,000 years. We hypothesize that the change in delta N-15 reflects the increasing influence of denitrified waters from the Eastern Tropical North Pacific and ongoing deoxygenation of the Eastern Pacific. When juxtaposed with other regional delta N-15 records our results further suggest that SBB is uniquely situated to record long-term change in the Eastern Tropical North Pacific.