ALBERT

Description: Observation‐based quantification of ocean carbon dioxide (CO 2 ) uptake relies on synthesis data sets such as the Surface Ocean CO 2 ATlas (SOCAT). However, the data collection effort has dramatically declined and the number of annual data sets in SOCATv2023 decreased by ∼35% from 2017 to 2021. This decline has led to a 65% increase (from 0.15 to 0.25 Pg C yr −1 ) in the standard deviation of seven SOCAT‐based air‐sea CO 2 flux estimates. Reducing the availability of the annual data to that in the year 2000 creates substantial bias (50%) in the long‐term flux trend. The annual mean CO 2 flux is insensitive to the seasonal skew of the SOCAT data and to the addition of the lower accuracy data set available in SOCAT. Our study highlights the need for sustained data collection and synthesis, to inform the Global Carbon Budget assessment, the UN‐led climate negotiations, and measurement, reporting, and verification of ocean‐based CO 2 removal projects. Plain Language Summary The Surface Ocean CO 2 ATlas (SOCAT) data set plays a crucial role in estimating the ocean carbon sink component of the Global Carbon Budget. However, the number of data sets available in SOCAT each year has drastically decreased since 2017. This study shows that the uncertainty in the data‐based ocean CO 2 flux estimate has increased by 65% due to this decline in data availability. The estimated fluxes, especially the long‐term flux trend, are remarkably affected by the data availability in SOCAT, reducing the reliability of ocean CO 2 uptake estimates in years and regions with sparse observations. Key Points Lower surface ocean f CO 2 data availability leads to higher uncertainty in data‐based estimates of ocean CO 2 uptake The long‐term trend in the ocean CO 2 flux increases by 1.5 times for subsequent years if the data availability is reduced to that in 2000 The annual mean CO 2 flux is not sensitive to the seasonal skew in the data and to the addition of low accuracy data

Description: Scientific Significance Statement Millions of predator–prey interactions between deep-diving toothed whales and cephalopods occur daily in the dark deep sea. While predatory whales developed traits to detect and hunt their prey, cephalopods had to expand their anti-predatory strategies specialized for visual predators, to counteract acoustic predators. Since toothed whale-cephalopod interactions have never been directly observed in the deep sea, it remains unknown what selective pressures and traits evolved from this arms race. Combining current knowledge, we formalize four hypotheses and associated research approaches that will guide future investigation on oceanic predator–prey systems. We identify whale echolocation as an unprecedented armament to hunt distant prey and propose that deep-sea squids avoid acoustic predators by (1) reducing their acoustic cross-section through body shape and posture, (2) deep-sea migration, and (3) not schooling. Toothed whale predation emerges as a potential driver of the cephalopod live-fast-die-young strategy—which may now leave cephalopods at competitive advantage under global change.

Description: Aims Within the intensively‐studied, well‐documented latitudinal diversity gradient, the deep‐sea biodiversity of the present‐day Norwegian Sea stands out with its notably low diversity, constituting a steep latitudinal diversity gradient in the North Atlantic. The reason behind this has long been a topic of debate and speculation. Most prominently, it is explained by the deep‐sea glacial disturbance hypothesis, which states that harsh environmental glacial conditions negatively impacted Norwegian Sea diversities, which have not yet fully recovered. Our aim is to empirically test this hypothesis. Specific research questions are: (1) Has deep‐sea biodiversity been lower during glacials than during interglacials? ( 2) Was there any faunal shift at the Mid‐Brunhes Event (MBE) when the mode of glacial–interglacial climatic change was altered? Location Norwegian Sea, deep sea (1819–2800 m), coring sites MD992277, PS1243, and M23352. Time period 620.7–1.4 ka (Middle Pleistocene–Late Holocene). Taxa studied Ostracoda (Crustacea). Methods We empirically test the deep‐sea glacial disturbance hypothesis by investigating whether diversity in glacial periods is consistently lower than diversity in interglacial periods. Additionally, we apply comparative analyses to determine a potential faunal shift at the MBE, a Pleistocene event describing a fundamental shift in global climate. Results The deep Norwegian Sea diversity was not lower during glacial periods compared to interglacial periods. Holocene diversity was exceedingly lower than that of the last glacial period. Faunal composition changed substantially between pre‐ and post‐MBE. Main conclusions These results reject the glacial disturbance hypothesis, since the low glacial diversity is the important precondition here. The present‐day‐style deep Norwegian Sea ecosystem was established by the MBE, more specifically by MBE‐induced changes in global climate, which has led to more dynamic post‐MBE conditions. In a broader context, this implies that the MBE has played an important role in the establishment of the modern polar deep‐sea ecosystem and biodiversity in general.

Description: The marine cyanobacterium Trichodesmium has the remarkable ability to interact with and utilize air‐borne dust as a nutrient source. However, dust may adversely affect Trichodesmium through buoyancy loss and exposure to toxic metals. Our study explored the effect of desert dust on buoyancy and mortality of natural Red Sea puff‐shaped Trichodesmium thiebautii . Sinking velocities and ability of individual colonies to stay afloat with increasing dust loads were studied in sedimentation chambers. Low dust loads of up to ∼400 ng per colony did not impact initial sinking velocity and colonies remained afloat in the chamber. Above this threshold, sinking velocity increased linearly with the colony dust load at a slope matching prediction based on Stoke's law. The potential toxicity of dust was assessed with regards to metal dissolution kinetics, differentiating between rapidly released metals, which may impact surface blooms, and gradually released metals that may impact dust‐centering colonies. Incubations with increasing dust concentrations revealed colony death, but the observed lethal dose far exceeded dust concentrations measured in coastal and open ocean systems. Removal of toxic particles as a mechanism to reduce toxicity was explored using SEM‐EDX imaging of colonies incubated with Cu‐minerals, yet observations did not support this pathway. Combining our current and former experiments, we suggest that in natural settings the nutritional benefits gained by Trichodesmium via dust collection outweigh the risks of buoyancy loss and toxicity. Our data and concepts feed into the growing recognition of the significance of dust for Trichodesmium 's ecology and subsequently to ocean productivity. Plain Language Summary Trichodesmium spp. are abundant cyanobacteria, forming extensive blooms in low latitude warm oceans, and contribute significantly to carbon (C) and nitrogen (N) fixation, recycling and export. Desert dust deposited on the ocean surface was shown to supply Trichodesmium with the scarce micronutrient iron. Spherical, millimeter‐sized colonies of Trichodesmium from different ocean basins were reported to actively accumulate dust in their cores. While dust accumulation likely helps Trichodesmium obtain nutrients, it may come at a cost. Metals released from dust may induce toxicity and the dust weight could send Trichodesmium to the ocean depth. Our experimental study with natural Red Sea colonies examined some trade‐offs of dust accumulation. Links between dust load and colony buoyancy were examined in sedimentation experiments. Toxicity thresholds for surface blooms and dust‐accumulating colonies were determined from mortality assays and dust dissolution measurements. We found that metal‐induced toxicity to Trichodesmium is unlikely at typical oceanic dust fluxes, and that dust‐containing colonies can remain buoyant. At high loads, dust weight determined the colony's sinking velocity. Our findings and concepts can be extended to additional aerosols and Trichodesmium ‐rich habitats, and may assist in assessing Trichodesmium 's distribution, ecophysiology, and contribution to C or N transport to the deep ocean. Key Points Dust collected by Trichodesmium colonies from seawater as a nutrient source may result in metal toxification and buoyancy loss At moderate dust loads, colonies kept their buoyancy, but above 400 ng, sinking velocities increased linearly with dust loads Desert dust induced Trichodesmium mortality through toxic metal release, yet the lethal dose far exceeded oceanic dust concentrations

Description: Every piece of plastic is made up of a unique combination of the host polymer, with some residual monomers or catalysts, as well as chemical additives added during processing of the plastic. This chapter aims to introduce plastic additives with a focus on their chemistry and function, transport and fate, detection in marine environments, and toxicities. The extensive list of additives can be simplified by dividing the types of additives into three groups: functional additives, colorants, and fillers/reinforcements. Plasticizers are added to plastics to improve their flexibility, durability, and elasticity over a broad range of temperatures while also reducing the glass transition temperature and the melt flow. Additives are well known to leach from plastics in the marine environment. Like their plastic counterparts, plastic additives are also susceptible to oxidative degradation and biodegradation. The toxicity of plastic additives is quite variable given the diversity of their chemical classes.

Description: Bacterial sulfate reduction (SR) is often determined by radiotracer techniques using 35S‐labeled sulfate. In environments featuring simultaneous sulfide oxidation, SR can be underestimated due to re‐oxidation of 35S‐sulfide. Recycling of 35S‐tracer is expected to be high in sediment with low concentrations of pore‐water sulfide and high abundance of giant filamentous sulfur‐oxidizing bacteria (GFSOB). Here, we applied a sulfide‐spiking method, originally developed for water samples, to sediments along a shelf‐slope transect (72, 128, 243, 752 m water depth) traversing the Peruvian oxygen minimum zone. Sediment spiked with unlabeled sulfide prior to 35S‐sulfate injection to prevent radiotracer recycling was compared to unspiked sediment. At stations characterized by low natural sulfide and abundant GFSOB (128 and 243 m), the method revealed 1–3 times higher SR rates in spiked sediment. Spiking had no effect on SR in sediment with high natural sulfide despite presence of GFSOB (72 m). Bioturbated sediment devoid of GFSOB (752 m) showed elevated SR in spiked samples, likely from artificial introduction of sulfidic conditions. Sulfide oxidation rates at the 128 and 243 m station, derived from the difference in SR between spiked and unspiked sediment, approximated rates of dissimilatory nitrate reduction to ammonium by GFSOB. Gross SR contributed considerably to benthic dissolved inorganic carbon fluxes at the three shallowest station, confirming that SR is an important process for benthic carbon respirations within the oxygen minimum zone. We recommend to further explore the spiking method to capture SR in sediment featuring low sulfide concentrations and high sulfur cycling by GFSOB.

Description: In the northeastern tropical Atlantic, a region of high potential vorticity (PV) determines the size of the exchange window for the interior thermocline flow of the subtropical cell via its variations in strength and extent. Variability of this PV barrier has the potential to impact the ventilation of the tropical Atlantic on decadal timescales. Here, the impact of the North Atlantic Oscillation (NAO) on the PV barrier related to isopycnals within the thermocline of the subtropical-tropical Atlantic Ocean is assessed from Argo observations for the time period of 2006-2022. Relative to the negative NAO phase (2009-2010), during the positive NAO phase (2014-2019), the North Atlantic subtropical high and the northeast trades are intensified. Satellite-derived wind stress curl shows increased upwelling/downwelling on the equatorward/poleward side of the trade wind zone, respectively. In the subtropical-tropical Atlantic, a symmetric pattern of isopycnal heave is observed: rising isopycnals within 20 degrees N and 20 degrees S and sinking poleward of that. With rising isopycnals, the PV barrier in the northeastern tropical Atlantic becomes stronger. Analyses of geostrophic velocities and the Sverdrup streamfunction show that during the positive NAO phase there are increased equatorward velocities at thermocline level along the western boundary and reduced velocities through the interior as a result of intensified northeast trades and therefore a strengthened PV barrier. Intensified trades lead to enhanced subduction of thermocline waters and, independent of that, to a strengthened Equatorial Undercurrent transport as observed at the mooring site at 0 degrees, 23 degrees W, likely via the pulling effect of the subtropical cells. In the North Atlantic Ocean, subducted water from the subtropics has two possible pathways within the thermocline toward the equatorial region: the interior pathway and the pathway along the western boundary. The size of the exchange window between subtropics and tropics depends on the extent of a barrier zone in the eastern part of the basin that is associated with wind-driven upwelling of density surfaces. The North Atlantic Oscillation (NAO) is the dominant atmospheric climate mode in the North Atlantic and in this study, we show how the NAO impacts the barrier for the equatorward thermocline flow in the tropical Atlantic Ocean. During positive NAO phases (e.g., 2014-2019), density surfaces become shallower and strengthen the barrier, while during negative NAO phases (e.g., 2009-2010) the barrier weakens. Geostrophic velocity analysis reveals that during positive NAO phases more thermocline water is transported equatorward via the western boundary and less via the interior pathway. Additionally, observations from a mooring site at 0 degrees, 23 degrees W show stronger Equatorial Undercurrent transport as a result of intensified trade winds during positive NAO phases. Trade winds in the northeastern tropical Atlantic strengthen during positive phases of the North Atlantic Oscillation (NAO+) Potential vorticity barrier for the interior equatorward thermocline flow of the North Atlantic Subtropical Cell strengthens during NAO+ Annual subduction of thermocline water and Equatorial Undercurrent transport increase simultaneously from 2008 to 2018

Description: Viscosity in the momentum equation is needed for numerical stability, as well as to arrest the direct cascade of enstrophy at grid scales. However, a viscous momentum closure tends to over-dissipate eddy kinetic energy. To return excessively dissipated energy to the system, the viscous closure is equipped with what is called dynamic kinetic energy backscatter. The amplitude of backscatter is based on the amount of unresolved kinetic energy (UKE). This energy is tracked through space and time via a prognostic equation. Our study proposes to add advection of UKE by the resolved flow to that equation to explicitly consider the effects of nonlocality on the subgrid energy budget. UKE can consequently be advected by the resolved flow before it is reinjected via backscatter. Furthermore, we suggest incorporating a stochastic element into the UKE equation to account for missing small-scale variability, which is not present in the purely deterministic approach. The implementations are tested on two intermediate complexity setups of the global ocean model FESOM2: an idealized channel setup and a double-gyre setup. The impacts of these additional terms are analyzed, highlighting increased eddy activity and improved flow characteristics when advection and carefully tuned, stochastic sources are incorporated into the UKE budget. Additionally, we provide diagnostics to gain further insights into the effects of scale separation between the viscous dissipation operator and the backscatter operator responsible for the energy injection. Oceanic swirls or "eddies" have a typical size of 10-100 km, which is close to the smallest scales that global ocean models commonly resolve. For physical and numerical reasons, these models require the addition of artificial terms that influence the flow near its smallest scales. Common approaches have the drawback of introducing systematic loss of kinetic energy contained in the eddies, which leads to errors that also affect the oceanic circulation on global scales. In our research, we compensate for this error by returning some of the missing energy back into the simulation, using a so-called kinetic energy backscatter scheme. In this work, we continue the development of an already existing and successful backscatter scheme, adding certain improvements to the way energy is budgeted and returned to the flow: we ensure that the local energy budget is attached to each fluid parcel as it is transported by the large-scale flow, and we also add a random forcing term that mimics unknown sources of such energy to bring its statistical properties closer to reality. We demonstrate that these modifications effectively improve the characteristics of the simulated flow. Extension of the subgrid energy equation of the kinetic energy backscatter parameterization by adding advection and a stochastic term Both additional terms improve several flow characteristics in two idealized test cases, a channel and a double-gyre Scale analysis reveals the necessity of sufficient scale separation between viscous energy dissipation and energy injection via backscatter. Key Points: - Extension of the subgrid energy equation of the kinetic energy backscatter parameterization by adding advection and a stochastic term - Both additional terms improve several flow characteristics in two idealized test cases, a channel and a double-gyre - Scale analysis reveals the necessity of sufficient scale separation between viscous energy dissipation and energy injection via backscatter

Description: The simulation of deep-sea conditions in laboratories is technically challenging but necessary for experiments that aim at a deeper understanding of physiological mechanisms or host-symbiont interactions of deep-sea organisms. In a proof-of-concept study, we designed a recirculating system for long-term culture (〉2 yr) of deep-sea mussels Gigantidas childressi (previously Bathymodiolus childressi). Mussels were automatically (and safely) supplied with a maximum stable level of ~60 μmol L−1 methane in seawater using a novel methane–air mixing system. Experimental animals also received daily doses of live microalgae. Condition indices of cultured G. childressi remained high over the years, and low shell growth rates could be detected, too, which is indicative of positive energy budgets. Using stable isotope data, we demonstrate that G. childressi in our culture system gained energy, both, from the digestion of methane-oxidizing endosymbionts and from digesting particulate food (microalgae). Limitations of the system, as well as opportunities for future experimental approaches involving deep-sea mussels, are discussed.

Description: We present a continuous ∼6.2 Ma long record of explosive activity from the Northwest Pacific volcanic arcs based on a composite tephra sequence derived from Ocean Drilling Program Sites 882A and 884B, and core MD01‐2416 on the Detroit Seamount. Geochemical fingerprinting of tephra glass using major and trace element analyses and correlations of tephra layers between the three cores allowed the identification of 119 unique tephras, suggesting eruptions of magnitude (M) of 5.8–7.8. Age estimates for all the identified eruptions were obtained with the help of published and further refined age models for the studied cores, direct 40 Ar/ 39 Ar dating of four ash layers, and Bayesian age modeling. The glass compositions vary from low‐ to high‐K 2 O basaltic andesite to rhyolite and exhibit typical subduction‐related affinity. The majority of the tephras originated from Kamchatka, only a few tephras—from the neighboring Kuril and Aleutian arcs. The glass compositions revealed no temporal trends but made it possible to identify their source volcanic zones in Kamchatka and, in some cases, to determine their source eruptive centers. Our data indicates episodes of explosive activity recorded in the Detroit tephra sequence at ∼6,200, 5,600–5,000, 4,300–3,700 ka, and almost continuous activity since ∼3,000 ka. Within the latter episode, the most active intervals can be identified at 1,700–1,600, 1,150–1,050, and 600–50 ka. Geochemically fingerprinted and dated Detroit tephra sequence form a framework for dating and correlating diverse paleoenvironmental archives across the Northwest Pacific and for studies of geochemical evolution of the adjacent volcanic arcs. Plain Language Summary Explosive volcanic eruptions produce defragmented material named tephra, which can be spread over large distances and form layers in sediments on ocean floor and continents. Long continuous tephra sequences preserved in marine sediments provide one of the best chronicles of the explosive eruptions, and allow detailed evaluation of their timing relative to climatic changes. We studied one of such natural records of explosive volcanism preserved in the sediments covering the Detroit Seamount in the Northwest Pacific. We identified 119 tephra layers, which have been buried in the sediments during the last 6.2 Ma and represent volcanic eruptions with ≥7 km 3 tephra volume. We analyzed geochemical composition and determined age of each tephra. Most tephras were found to originate from volcanoes in Kamchatka, a few from the Kuril and Aleutian volcanoes. We found that the explosive activity recorded in the Detroit tephra sequence was not uniform over time. It peaked at ∼6,200, 5,600–5,000, 4,300–3,700, has continued since ∼3,000 thousand years ago until present. All tephra layers from our study can be used as unique isochrons for dating and correlating paleoenvironmental archives across the Northwest Pacific and for the reconstruction of the detailed volcanic record in the Earth history. Key Points We report age and composition for 119 tephras from sediment cores representing ∼6.2 Ma record of explosive volcanism in the NW Pacific The tephras have subduction‐related origin and mostly originate from volcanic eruptions with magnitude (M) of 5.8–7.8 in Kamchatka The data indicates episodes of explosive activity at ∼6,200, 5,600–5,000, 4,300–3,700 ka, and almost continuous activity since ∼3,000 ka