Global Quaternary Carbonate Burial: Proxy- and Model-Based Reconstructions and Persisting Uncertainties.

Constraining rates of marine carbonate burial through geologic time is critical for interpreting reconstructed changes in ocean chemistry and understanding feedbacks and interactions between Earth's carbon cycle and climate. The Quaternary Period (the past 2.6 million years) is of particular interest due to dramatic variations in sea level that periodically exposed and flooded areas of carbonate accumulation on the continental shelf, likely impacting the global carbonate budget and atmospheric carbon dioxide. These important effects remain poorly quantified. Here, we summarize the importance of carbonate burial in the ocean-climate system, review methods for quantifying carbonate burial across depositional environments, discuss advances in reconstructing Quaternary carbonate burial over the past three decades, and identify gaps and challenges in reconciling the existing records. Emerging paleoceanographic proxies such as the stable strontium and calcium isotope systems, as well as innovative modeling approaches, are highlighted as new opportunities to produce continuous records of global carbonate burial.

Insights into the deglacial variability of phytoplankton community structure in the eastern equatorial Pacific Ocean using [231Pa/230Th]xs and opal-carbonate fluxes.

Fully and accurately reconstructing changes in oceanic productivity and carbon export and their controls is critical to determining the efficiency of the biological pump and its role in the global carbon cycle through time, particularly in modern CO2 source regions like the eastern equatorial Pacific (EEP). Here we present new high-resolution records of sedimentary 230Th-normalized opal and nannofossil carbonate fluxes and [231Pa/230Th]xs ratios from site MV1014-02-17JC in the Panama Basin. We find that, across the last deglaciation, phytoplankton community structure is driven by changing patterns of nutrient (nitrate, iron, and silica) availability which, in turn, are caused by variability in the position of the Intertropical Convergence Zone (ITCZ) and associated changes in biogeochemical cycling and circulation in the Southern Ocean. Our multi-proxy work suggests greater scrutiny is required in the interpretation of common geochemical proxies of productivity and carbon export in the EEP.

Impact of local rivers on coastal acidification.

Coastal ecosystems are highly dynamic areas for carbon cycling and are likely to be negatively impacted by increasing ocean acidification. This research focused on dissolved inorganic carbon (DIC) and total alkalinity (TA) in the Mississippi Sound to understand the influence of local rivers on coastal acidification. This area receives large fluxes of freshwater from local rivers, in addition to episodic inputs from the Mississippi River through a human-built diversion, the Bonnet Carré Spillway. Sites in the Sound were sampled monthly from August 2018 to November 2019 and weekly from June to August 2019 in response to an extended spillway opening. Prior to the 2019 spillway opening, the contribution of the local, lower alkalinity rivers to the Sound may have left the study area more susceptible to coastal acidification during winter months, with aragonite saturation states (Ωar) < 2. After the spillway opened, despite a large increase in TA throughout the Sound, aragonite saturation states remained low, likely due to hypoxia and increased CO2 concentrations in subsurface waters. Increased Mississippi River input could represent a new normal in the Sound's hydrography during spring and summer months. The spillway has been utilized more frequently over the last two decades due to increasing precipitation in the Mississippi River watershed, which is primarily associated with climate change. Future increases in freshwater discharge and the associated declines in salinity, dissolved oxygen, and Ωar in the Sound will likely be detrimental to oyster stocks and the resilience of similar ecosystems to coastal acidification.

Coordinated regulation of growth, activity and transcription in natural populations of the unicellular nitrogen-fixing cyanobacterium Crocosphaera.

The temporal dynamics of phytoplankton growth and activity have large impacts on fluxes of matter and energy, yet obtaining in situ metabolic measurements of sufficient resolution for even dominant microorganisms remains a considerable challenge. We performed Lagrangian diel sampling with synoptic measurements of population abundances, dinitrogen (N2) fixation, mortality, productivity, export and transcription in a bloom of Crocosphaera over eight days in the North Pacific Subtropical Gyre (NPSG). Quantitative transcriptomic analyses revealed clear diel oscillations in transcript abundances for 34% of Crocosphaera genes identified, reflecting a systematic progression of gene expression in diverse metabolic pathways. Significant time-lagged correspondence was evident between nifH transcript abundance and maximal N2 fixation, as well as sepF transcript abundance and cell division, demonstrating the utility of transcriptomics to predict the occurrence and timing of physiological and biogeochemical processes in natural populations. Indirect estimates of carbon fixation by Crocosphaera were equivalent to 11% of net community production, suggesting that under bloom conditions this diazotroph has a considerable impact on the wider carbon cycle. Our cross-scale synthesis of molecular, population and community-wide data underscores the tightly coordinated in situ metabolism of the keystone N2-fixing cyanobacterium Crocosphaera, as well as the broader ecosystem-wide implications of its activities.

A stagnation event in the deep South Atlantic during the last interglacial period.

During the last interglacial period, global temperatures were ~2°C warmer than at present and sea level was 6 to 8 meters higher. Southern Ocean sediments reveal a spike in authigenic uranium 127,000 years ago, within the last interglacial, reflecting decreased oxygenation of deep water by Antarctic Bottom Water (AABW). Unlike ice age reductions in AABW, the interglacial stagnation event appears decoupled from open ocean conditions and may have resulted from coastal freshening due to mass loss from the Antarctic ice sheet. AABW reduction coincided with increased North Atlantic Deep Water (NADW) formation, and the subsequent reinvigoration in AABW coincided with reduced NADW formation. Thus, alternation of deep water formation between the Antarctic and the North Atlantic, believed to characterize ice ages, apparently also occurs in warm climates.

Using software-based simulation for resident physician training in the management of temporary pacemakers.

INTRODUCTION: An understanding of epicardial pacing is essential for the postoperative management of patients having cardiac surgery. By developing a software-based epicardial pacing program to be used with the existing patient simulator, resident physicians may be exposed to various clinical scenarios that might be encountered while caring for a postoperative heart patient. This experience will assist junior residents with no prior experience to become familiar and competent in the management of epicardial pacemakers. METHODS: The simulation session used the human patient simulator in combination with an internally developed computer program using Flash animation to present arrhythmias and various epicardial pacing interventions commonly used in the postoperative period. By modeling the Flash animation software after a pulse generator, the user is able to make adjustments (type of pacing, rate of pacing, and chamber output) as if using an actual pulse generator. A group of 15 anesthesiology residents who had minimal or no epicardial pacing experience underwent the simulation training. Feedback was obtained by an anonymous postscenario questionnaire. RESULTS: A detailed description of the scenario and computer program is provided. All participants provided positive feedback and have strongly agreed that the simulation session improved their understanding and management of epicardial pacemakers. CONCLUSIONS: Our experience with epicardial pacing simulation was demonstrated to be effective in increasing the confidence of junior anesthesiology residents with little or no prior experience with regard to the management of temporary pacemakers.

Neurophysiological monitoring simulation using flash animation for anesthesia resident training.

INTRODUCTION: Surgery of the spine is associated with the possible complication of permanent nerve injury. Neurophysiological monitoring is widely used during spine surgery to decrease the incidence and severity of neurologic injury. A profound understanding of physiological and pharmacological factors influencing evoked potentials is expected from the anesthesia provider. METHODS: Because demonstration and teaching of all somatosensory evoked potential (SSEP) changes is difficult in the clinical environment, we developed human patient simulator scenarios to facilitate the anesthesia resident training in neurophysiological monitoring. A SSEP simulation for resident training was created using flash animation in a patient simulation program and is the focus of this report. Feedback from participants (anesthesia residents) was obtained by a postscenario survey. RESULTS: This report provides a detailed description of the scenario and computer program. The survey findings indicated that the simulation session is an effective teaching method of SSEP monitoring. CONCLUSION: Flash animation integration into a patient simulation program for SSEP monitoring appears to be an effective method for anesthesia resident education in neurophysiological monitoring.