ALBERT

Description: Plankton is a massive and phylogenetically diverse group of thousands of prokaryotes, protists (unicellular eukaryotic organisms), and metazoans (multicellular eukaryotic organisms; Fig. 1). Plankton functional diversity is at the core of various ecological processes, including productivity, carbon cycling and sequestration, nutrient cycling (Falkowski 2012), interspecies interactions, and food web dynamics and structure (D'Alelio et al. 2016). Through these functions, plankton play a critical role in the health of the coastal and open ocean and provide essential ecosystem services. Yet, at present, our understanding of plankton dynamics is insufficient to project how climate change and other human-driven impacts affect the functional diversity of plankton. That limits our ability to predict how critical ecosystem services will change in the future and develop strategies to adapt to these changes.

Description: Key Points: - High resolution carbonate chemistry, δ13C-DIC, and particle flux measurements in the NE Pacific sheds light on the upper oceancalcium carbonate and alkalinity cycles. - Based on this sampling campaign, there isevidence for substantial CaCO3 dissolution in the mesopelagic zone above the saturation horizon. - Dissolution experiments, observations, and modeling suggest that shallow CaCO3 dissolutionis coupled to the consumption of organic carbon, through a combination of zooplankton grazing and oxic respiration within particle microenvironments. 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 situcoccolith 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 ratesof all three major calcifying groups (coccoliths, foraminifera, and aragonitic pteropods)aretoo slow to explainthe patternsofboth CaCO3sinking fluxand alkalinity regenerationin the NorthPacific.Usinga combination of dissolved and solid-phase tracers, we document a significant dissolution signal in seawater supersaturated for calcite. Driving CaCO3dissolutionwith acombination of ambient saturation state and oxygen consumption simultaneously explainssolid-phase CaCO3flux profiles and patterns of alkalinity regeneration across the entire N. Pacific basin. Wedo not need to invokethe presence ofcarbonate phases with higher solubilities.Instead, biomineralization and metabolic processesintimately associatethe acid (CO2) and the base (CaCO3) in the same particles,driving the coupled shallow remineralization of organic carbonand CaCO3.The linkage of these processes likely occurs through a combination of dissolution due to zooplankton grazing and microbial aerobic respiration withindegrading particle aggregates.The coupling of these cyclesacts as a major filter on the export of both organic and inorganic carbon to the deep ocean.

Description: Natural forcing from solar and volcanic activity contributes significantly to climate variability. The post-eruption cooling of strong volcanic eruptions was hypothesized to have led to millennial-scale variability during Glacials. Cooling induced by volcanic eruption is potentially weaker in the warmer climate. The underlying question is whether the climatic response to natural forcing is state-dependent. Here, we quantify the response to natural forcing under Last Glacial and Pre-Industrial conditions in an ensemble of climate model simulations. We evaluate internal and forced variability on annual to multicentennial scales. The global temperature response reveals no state dependency. Small local differences result mainly from state-dependent sea ice changes. Variability in forced simulations matches paleoclimate reconstructions significantly better than in unforced scenarios. Considering natural forcing is therefore important for model-data comparison and future projections. Key Points We present Glacial/Interglacial climate simulations and quantify effects of time-varying volcanic and solar forcing on climate variability The mean global and local response to these forcings is similar in Glacial and Interglacial climate, suggesting low state dependency In both climate states, modeled temperature variance agrees better with palaeoclimate data when volcanic and solar forcing is included

Description: Multiyear turbulence measurements from oceanographic moorings in equatorial Atlantic and Pacific cold tongues reveal similarities in deep cycle turbulence (DCT) beneath the mixed layer (ML) and above the Equatorial Undercurrent (EUC) core. Diurnal composites of turbulence kinetic energy dissipation rate, ϵ, clearly show the diurnal cycles of turbulence beneath the ML in both cold tongues. Despite differences in surface forcing, EUC strength and core depth DCT occurs, and is consistent in amplitude and timing, at all three sites. Time-mean values of ϵ at 30 m depth are nearly identical at all three sites. Variations of averaged values of ϵ in the deep cycle layer below 30 m range to a factor of 10 between sites. A proposed scaling in depth that isolates the deep cycle layers and of ϵ by the product of wind stress and current shear collapses vertical profiles at all sites to within a factor of 2.

Description: Given the accelerating rate of biodiversity loss, the need to prioritize marine areas for protection represents a major conservation challenge. The three-dimensionality of marine life and ecosystems is an inherent element of complexity for setting spatial conservation plans. Yet, the confidence of any recommendation largely depends on shifting climate, which triggers a global redistribution of biodiversity, suggesting the inclusion of time as a fourth dimension. Here, we developed a depth-specific prioritization analysis to inform the design of protected areas, further including metrics of climate-driven changes in the ocean. Climate change was captured in this analysis by considering the projected future distribution of 〉2000 benthic and pelagic species inhabiting the Mediterranean Sea, combined with climatic stability and heterogeneity metrics of the seascape. We identified important areas based on both biological and climatic criteria, where conservation focus should be given in priority when designing a three-dimensional, climate-smart protected area network. We detected spatially concise, conservation priority areas, distributed around the basin, that protected marine areas almost equally across all depth zones. Our approach highlights the importance of deep sea zones as priority areas to meet conservation targets for future marine biodiversity, while suggesting that spatial prioritization schemes, that focus on a static two-dimensional distribution of biodiversity data, might fail to englobe both the vertical properties of species distributions and the fine and larger-scale impacts associated with climate change.

Description: The intraplate Hawaiian-Emperor Seamount Chain has long been considered a hotspot track generated by the motion of the Pacific plate over a deep mantle plume, and an ideal feature therefore for studies of volcanic structure, magma supply, plume-crust interaction, flexural loading, and upper mantle rheology. Despite their importance as a major component of the chain, the Emperor Seamounts have been relatively little studied. In this paper, we present the results of an active-source wide-angle reflection and refraction experiment conducted along an ocean-bottom-seismograph (OBS) line oriented perpendicular to the seamount chain, crossing Jimmu guyot. The tomographic P wave velocity model, using ∼20,000 travel times from 26 OBSs, suggests that there is a high-velocity (〉6.0 km/s) intrusive core within the edifice, and the extrusive-to-intrusive ratio is estimated to be ∼2.5, indicating that Jimmu was built mainly by extrusive processes. The total volume for magmatic material above the top of the oceanic crust is ∼5.3 × 104 km3, and the related volume flux is ∼0.96 m3/s during the formation of Jimmu. Under volcanic loading, the ∼5.3-km-thick oceanic crust is depressed by ∼3.8 km over a broad region. Using the standard relationships between Vp and density, the velocity model is verified by gravity modeling, and plate flexure modeling indicates an effective elastic thickness (Te) of ∼14 km. Finally, we find no evidence for large-scale magmatic underplating beneath the pre-existing crust.

Description: Plate divergence along mid-ocean ridges is accommodated through faulting and magmatic accretion, and, at overlapping spreading centers (OSC), is distributed across two curvilinear overlapping ridge axes. One-meter resolution bathymetry acquired by autonomous underwater vehicles, combined with distribution and ages of lava flows, is used to: (1) analyze the spatial and temporal distribution of flows, faults, and fissures in the OSC between the distal south rift zone of Axial Seamount and the Vance Segment, (2) locate spreading axes, (3) calculate extension, and (4) determine the proportion of extension accommodated at the surface by faults and fissures versus volcanic extrusion over a period of ∼1300-1450 years. Our study reveals that in the recent history of the ridges, extension over a distance of 14 km across the Axial/Vance OSC was asymmetric in proportion and style: faults and fissures across 1-2 km of the Vance axial valley accommodated ∼3/4 of the spreading, whereas dike-fed eruptions contributed ∼1/4 of the extension and occurred across 4 km of the south rift of Axial Seamount.