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Global climate changes, such as warming and ocean acidification (OA), are likely to negatively impact calcifying marine taxa. Abundant and ecologically important coralline algae may be particularly susceptible to OA; however, multi-stressor studies and those on articulated morphotypes are lacking. Here, we use field observations and laboratory experiments to elucidate the impacts of warming and acidification on growth, calcification, mineralogy, and photophysiology of the temperate articulated coralline alga, Calliarthron tuberculosum. We conducted a 4-week fully factorial mesocosm experiment exposing individuals from a southern CA kelp forest to current and future temperature and pH/pCO

Mesoscale geostrophic vortices are an important oceanographic feature in the Guaymas Basin (GB). Depending on the depth, bathymetry, coastline, local wind, and surface current conditions, they exhibit different behavior. Their size and direction of rotation are forced mainly by the Eastern Tropical Pacific Ocean (ETPO), with some contribution from monsoonal winds. Cyclonic vortices cause divergence, advecting nutrients into the photic zone and stimulating productivity; in contrast, anticyclonic vortices induce convergence at the surface and produce down-welling and surface layers poor in nitrates and chlorophylls, but they transport and disperse upwelled waters enriched in nutrients from the east to the west side. Anticyclonic vortices dominate the circulation in October, but vortices of either sign can be present from November to March. This research aims to investigate productivity fluctuations in the west side of the Guaymas Basin, understand the role of mesoscale vortices and the link with a mesoscale remote forcing in the ETPO during the past 31,000 yr based on biogenic opal and Ba/Ti ratio records in Hole 1545A (~42 mbsf) of IOPD Expedition 385. This period comprises significant climatic events, including the Last Glacial Maximum (LGM), the deglacial to Holocene transition, the Holocene thermal maximum (HTM), and changes in North America Monsoon (NAM). The age model was based on 17 radiocarbon AMS analyses on bulk sediments. We used a Bayesian statistics approach with the R package “Bacon” using the Marine 20 calibration curve and a regional reservoir-age correction (∆R) 301 ± 50 yr. The records show an increase in productivity from ~ 31,000 to 28,300 yr in the early stage of MIS 2, which then declines markedly during the LGM (26,000 to 19,000 yr), reaching its minimum value of ~25,000 yr. This pattern might be related to the expansion of the Polar Cell that caused the southerly migration of the North Pacific High (NPH) system, weakening the vortices, changing NW wind strengths, and reducing wind-driven upwelling in the eastern margin, causing low productivity. In addition, at that time, the poleward coastal circulation transported nutrient-poor waters from the ETPO. During the deglaciation, records show increased productivity, with high opal values between 16,000 and 15,000 yr. A gradual increase in productivity is observed from the glacial to the Holocene, particularly during HTM between 10,500 and 8,000 yr. From ~ 7,000 to 2,200 yr, a gradual productivity decrease might be related to the NAM onset (~ 6,000 yr). For the last 3,000 cal yr BP productivity increased, but with important fluctuations. We hypothesize that productivity in the northwestern Guaymas Basin during the last 31,000 yr has been controlled mainly by mesoscale vortices, linked with a mesoscale remote forcing in the tropical Pacific coast and with a local mesoscale forcing of the wind, rather than by upwelling.

We investigated the changes in water masses circulation patterns in the Guaymas Basin in the Gulf of California to reveal the oceanographic and climatic evolution. We analyzed silica microfossils: Polycystine Radiolaria (hereafter radiolarians), and silicoflagellates, in the sediments of the deep-sea cores from Site U1545-A (~42 mbsf) of the IODP Expedition 385, collected on the west side of the basin.The age model is based on 17 AMS radiocarbon dates covering the last 31,000 yr, between MIS (Marine Isotope Stage) 3 and MIS 1. Sedimentation rates ranged between 0.88 to 2.02 mm/yr. The highest sedimentation rates (ranging from 1.61 to 2.1 mm/yr) are between ∼31,000 and 19,000 yr (including the Last Glacial Maximum, LGM), coinciding with falling sea level and a maximum ice volume. A total of 122 samples were analyzed, and 145 radiolarian taxa and 16 silicoflagellate species were identified. Radiolarians are rich, diverse, and well-preserved; overall, diversity is much higher for the last 15,000 yr.Factor analysis of radiolarian assemblages suggested regional oceanic patterns based on environmental affinities. The dominance of Siphocampe lineata, intermediate dweller radiolarian, was evident in the transition of MIS 3 to MIS 2, suggesting a significant influence of the Pacific Intermediate Water prior to the Last Glacial Maximum (LGM) and in Heinrich-1 (H-1), probably due to stronger North Pacific Intermediate Water (NPIW) formation. Besides, during the LGM, surface radiolarians assemblage and silicoflagellate specie such as Cycladophora davisiana and Botryostrobus aquilonaris, and Octactis speculum, supports the idea of an incursion of the California Current Water (CCW) into GB, possibly by the southward shift migration of the NPH (North Pacific High) system, caused by the polar jet displacement and, because of the weakened NW-winds as well as the strengthened poleward circulation into the gulf.The assemblage of Tetrapyle octacantha group and Phorticium pylonium group, surface dwellers radiolarians, and the silicoflagellate Dictyocha fibula var. messanensis indicated the dominance of Tropical Surface Water related to warm conditions and the influence of tropical water incursions enhanced by the Costa Rica Current. This association becomes more evident during the BA (Bolling Allerod) and the Holocene, mainly during the HTM (Holocene Thermal Maximum).Surface dwellers species (Lithomelissa setosa, L. thoracites, Peridium longispinum, and Octactis octonaria), associated with the Gulf of California Water prevailed in episodic intervals during the late Pleistocene and the Holocene, suggesting mixed-water species. Due to an increase in evaporation processes in the gulf caused by the strength of NW winds and winter convection in the gulf, the dominance of this water mass may have occurred synchronously with the Monsoon System shift during the Holocene.

The Guaymas Basin in the Gulf of California represents the nascent stage of an ocean, characterized by siliceous organic-rich sediments (diatom ooze) deposited at very high sedimentation rates. The basin is also characterized by a dense network of shallow mid-Pleistocene to recent sills that have intruded the subseafloor over a distance of several tens of kilometers from the spreading axis. These magmatic intrusions produce heat anomalies and sediment transformations in the contact aureoles that affect both organic and inorganic compounds, such as cracking of sediment OM, dehydration and dissolution of mineral phases, creation of porosity and convection of hydrothermal fluids. We focus our investigations on the phyllosilicates (clay minerals) that formed at the contact between the sill and the sediment (IODP Expedition 385, Sites U1546 and U1550): overall our results support the intepretation that these hydrated minerals can be used as proxies for fluid-rock interactions. In our study, we investigate sediment and sill samples from the contact zones by combining XRD analysis of oriented samples (< 2 and Authigenic phyllosilicates are abundant at sediment-sill interface, they registered the last stages of the fluid-rock interaction probably related to hydrothermal fluid circulation.

Igneous sill intrusions into young organic-rich sedimentary basins have major impact on the carbon cycle but also on the transfer of major and trace element between deep and superficial geological reservoirs. The Guaymas Basin in the Gulf of California represents the nascent stage of an ocean characterized by siliceous organic-rich sediments (diatom ooze) deposited at high sedimentation rates. A very dense network of shallow sill intrusions recently invaded the basin. We focused on Site U1546 (Holes A and C) located at about ~51 km northwest of the axial graben of the northern Guaymas Basin spreading segment; this site recovered 540m of sediments and an 80m-thick sill located at 350-430 meters below the seafloor (mbsf). The relatively high geothermal gradient (> 200 °C/km) induces measurable diagenetic transformations in sediments, involving sulfides, carbonates and silica (and clay minerals). Based on retrieved materials from IODP Expedition 385, we present here geochemical and mineralogical characterization of the sedimentary intervals at sill contacts. Our results indicate that sulfides and silica polymorphs are the main phases impacted by contact metamorphism. The transition between opal CT-quartz and pyrite-pyrrhotite is observed in the contact aureoles. In the upper aureole, authigenic quartz and disseminated 20-50 micron pyrrhotite partly fill secondary pores and detrital feldspars are partially dissolved. Patchy carbonate also fills primary interparticle sediment pores just above the contact. In the lower contact aureole, quartz and 200-micron-size euhedral crystals of pyrrhotite are also present. Additionally, a significant metasomatism is observed in the lower contact-aureole meta-sediments with authigenic plagioclase precipitated around detrital feldspars and locally euhedral pyroxenes included in patches of carbonate cement; this suggests precipitation by late to post magmatic fluids at T>300°C. The lower contact aureole is also more enriched in CaO, Na2O, Fe2O3 and trace elements (Cu, As, Zn…). Based on these petrological investigations a new conceptual model of magma sediment fluid interactions will be proposed.

The diagenesis of biogenic silica is arguably one of the most significant early diagenetic processes in the shallow subseafloor and can also have profound implication for the routing of magma in rift basins. The transformation of glass-like amorphous silica (opal-A) in diatoms and radiolarians into crystalline forms (opal-CT) converts soft and watery biogenic oozes into harder sedimentary rocks. The silica diagenetic front is extensive (km-scale) forming prominent seismic reflectors, causes regional-scale differential compaction, subsidence, and the expulsion of pore fluids. Most importantly, it corresponds to changes in sediment rheology from ductile oozes to brittle, fracture-prone and more permeable sedimentary rocks. The relationships between silica diagenesis and subseafloor magmatism have been investigated by Expedition 385 of the Integrated Ocean Discovery Program (IODP) in the off-axis region Guaymas Basin (GB) of the Gulf of California at the neighboring Sites U1545 and U1546, the latter including a ~70 m-thick sill intrusion, and at Site U1547, where the top of a massive sill was recovered at shallower depths. The lithostratigraphic and mineralogic analyses of the cores recovered by the expedition combined with interstitial water geochemistry and physical properties unveil a new and somewhat unexpected picture of the GB’s subseafloor environment. The first discovery is that despite the super-fast sedimentation/burial (up to 1m/kyr) and the very high geothermal gradients, the transformation of opal-A to opal-CT occurs at ~75 ºC or higher in situ temperatures which is much hotter (and deeper) than expected based on previous deep-sea core studies, outcrop studies, laboratory experiments or calculated by models. We hypothesize that the apparent ‘sluggishness’ of silica transformation is the result of the current kinetic model not being able to predict this transformation when burial rates are much faster than typical biogenic sediments in open ocean conditions for which they were originally created. The second important finding relates the Opal CT-zone with magma intrusions. The massive sill at Site U1546 splits the opal-CT zone, though the latter has identical characteristics (e.g. total thickness, gradual increase in silica crystallization with depth) as the opal-CT zone at the nearby Site U1545, located just outside the extent of the sill. Moreover, the sill intrusion is much shallower at Site U1547 where the opal-CT zone is also shallower due to the higher geothermal gradient (~510 Cº/km as opposed to ~100 ºC/km at Site U1546). Not only these observations suggest that the sill formation postdates the silica phase change, but also that this diagenetic interface controls the way magma moves in the GB subseafloor whereby the opal-A/opal-CT transition zone acts as major physical anisotropy in the sedimentary column to reroute magma from vertical to lateral movement. In conclusion, this study greatly expands the range of depths/temperatures at which amorphous silica can persists in the subseafloor and establishes fascinating connections between seemingly disconnected processes in the natural world: surface water biological productivity and crustal architecture of a newborn ocean.