Evaluating experiential education through an intertidal ecology field trip.

*Background/Question/Methods*

Stanford SEEDS and the Jasper Ridge Biological Preserve have worked together with Redwood High School to implement an experiential ecology education program. The Redwood Environmental Academy of Leadership(REAL) is designed to bring underserved high school students out of the classroom and into the outdoors to create a unique and effective learning experience. Though the program focuses on riparian ecosystem restoration, the course curriculum is interdisciplinary and designed to inspire continuation high school students to attend college or pursue environmental careers. Through a SEEDS special grant, REAL students were taken to Fitzgerald Marine Reserve in Half Moon Bay, California, to learn about marine ecology and intertidal ecosystems at a minus tide. Redwood High School students were joined by their teachers and Stanford faculty and students to study the adaptations of intertidal organisms to their harsh environment.

*Results/Conclusions*

SEEDS and REAL were able to evaluate the success of the field trip by comparing the students’ knowledge of intertidal habitat, the nature of the ocean ecosystems, plants, animals, and reproduction both before and after the trip. This opportunity provides insight into the effectiveness of experiential education for the REAL program and recommendations for future ecology outreach programs

Coastal Upwelling Enhances Abundance of a Symbiotic Diazotroph (UCYN-A) and Its Haptophyte Host in the Arctic Ocean

The apparently obligate symbiosis between the diazotroph Candidatus Atelocyanobacterium thalassa (UCYN-A) and its haptophyte host, Braarudosphaera bigelowii, has recently been found to fix dinitrogen (N2) in polar waters at rates (per cell) comparable to those observed in the tropical/subtropical oligotrophic ocean basins. This study presents the novel observation that this symbiosis increased in abundance during a wind-driven upwelling event along the Alaskan Beaufort shelfbreak. As upwelling relaxed, the relative abundance of B. bigelowii among eukaryotic phytoplankton increased most significantly in waters over the upper slope. As the host’s nitrogen demands are believed to be supplied primarily by UCYN-A, this response suggests that upwelling may enhance N2 fixation as displaced coastal waters are advected offshore, potentially extending the duration of upwelling-induced phytoplankton blooms. Given that such events are projected to increase in intensity and number with ocean warming, upwelling-driven N2 fixation as a feedback on climate merits investigation

The influence of winter water on phytoplankton blooms in the Chukchi Sea

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 118 (2015): 53-72, doi:10.1016/j.dsr2.2015.06.006.The flow of nutrient-rich winter water (WW) through the Chukchi Sea plays an important and previously uncharacterized role in sustaining summer phytoplankton blooms. Using hydrographic and biogeochemical data collected as part of the ICESCAPE program (June-July 2010-11), we examined phytoplankton bloom dynamics in relation to the distribution and circulation of WW (defined as water with potential temperature ≤ -1.6°C) across the Chukchi shelf. Characterized by high concentrations of nitrate (mean: 12.3 ± 5.13 μmol L-1) that typically limits primary production in this region, WW was correlated with extremely high phytoplankton biomass, with mean chlorophyll a concentrations that were three-fold higher in WW (8.64 ± 9.75 μg L-1) than in adjacent warmer water (2.79 ± 5.58 μg L-1). Maximum chlorophyll a concentrations (~30 μg L-1) were typically positioned at the interface between nutrient-rich WW and shallower, warmer water with more light availability. Comparing satellite-based calculations of open water duration to phytoplankton biomass, nutrient concentrations, and oxygen saturation revealed widespread evidence of under-ice blooms prior to our sampling, with biogeochemical properties indicating that blooms had already terminated in many places where WW was no longer present. Our results suggest that summer phytoplankton blooms are sustained for a longer duration along the pathways of nutrient-rich WW and that biological hotspots in this region (e.g. the mouth of Barrow Canyon) are largely driven by the flow and confluence of these extremely productive pathways of WW that flow across the Chukchi shelf.This material is based upon work supported by the National Aeronautic and Space Administration (NASA) under Grant No. NNX10AF42G and the National Science Foundation Graduate Research Fellowship under Grant No. DGE-0645962 to K.E. Lowry

Under-ice phytoplankton blooms inhibited by spring convective mixing in refreezing leads

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 90–109, doi:10.1002/2016JC012575.Spring phytoplankton growth in polar marine ecosystems is limited by light availability beneath ice-covered waters, particularly early in the season prior to snowmelt and melt pond formation. Leads of open water increase light transmission to the ice-covered ocean and are sites of air-sea exchange. We explore the role of leads in controlling phytoplankton bloom dynamics within the sea ice zone of the Arctic Ocean. Data are presented from spring measurements in the Chukchi Sea during the Study of Under-ice Blooms In the Chukchi Ecosystem (SUBICE) program in May and June 2014. We observed that fully consolidated sea ice supported modest under-ice blooms, while waters beneath sea ice with leads had significantly lower phytoplankton biomass, despite high nutrient availability. Through an analysis of hydrographic and biological properties, we attribute this counterintuitive finding to springtime convective mixing in refreezing leads of open water. Our results demonstrate that waters beneath loosely consolidated sea ice (84–95% ice concentration) had weak stratification and were frequently mixed below the critical depth (the depth at which depth-integrated production balances depth-integrated respiration). These findings are supported by theoretical model calculations of under-ice light, primary production, and critical depth at varied lead fractions. The model demonstrates that under-ice blooms can form even beneath snow-covered sea ice in the absence of mixing but not in more deeply mixed waters beneath sea ice with refreezing leads. Future estimates of primary production should account for these phytoplankton dynamics in ice-covered waters.National Science Foundation (NSF) Grant Numbers: PLR-1304563 , PLR-1303617; KEL; NSF Graduate Research Fellowship Program Grant Number: DGE-06459622018-07-0

Effects of Iron and Light Availability on Phytoplankton Photosynthetic Properties in the Ross Sea

Waters of the Southern Ocean are characterized by high macronutrient concentrations but limited availability of trace metals and light, often making it difficult for phytoplankton to achieve maximum growth rates. One strategy employed by Southern Ocean phytoplankton in culture to cope with low light and low dissolved iron (DFe) is to enhance light absorption by increasing their antenna size rather than the number of reaction centers, thereby reducing their Fe demand. Here we provide physiological evidence that natural populations of Southern Ocean phytoplankton employ a similar photoacclimation strategy to cope with low ambient DFe concentrations. During a research cruise to the Ross Sea in 2013-2014, we conducted 4 bioassay experiments in which we manipulated light and DFe concentrations and measured changes in phytoplankton biomass, growth rate, photosynthetic parameters, fluorescence parameters, and pigment composition. Phytoplankton responded strongly to DFe additions, exhibiting significantly higher biomass, growth rates, and photosynthetic competency. At low light, the maximum photosynthetic rate (P*max) was significantly reduced and the photosynthetic efficiency (α*) was unchanged compared to the high light treatment, regardless of phytoplankton species composition or DFe concentration. Our data suggest that Southern Ocean phytoplankton have evolved an Fe-saving strategy whereby they photoacclimate to low light by increasing their photosynthetic unit size, rather than photosynthetic unit number, even when DFe is available. It appears this Fe-saving strategy is characteristic of both Phaeocystis antarctica and diatoms, suggesting that it is a common adaptation among phytoplankton taxa that grow under Fe limitation in the Southern Ocean

Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ashley, K. E., McKay, R., Etourneau, J., Jimenez-Espejo, F. J., Condron, A., Albot, A., Crosta, X., Riesselman, C., Seki, O., Mass, G., Golledge, N. R., Gasson, E., Lowry, D. P., Barrand, N. E., Johnson, K., Bertler, N., Escutia, C., Dunbar, R., & Bendle, J. A. Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat. Climate of the Past, 17(1), (2021): 1-19, https://doi.org/10.5194/cp-17-1-2021.Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (∼ 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.This research has been supported by the Natural Environment Research Council (CENTA PhD; NE/L002493/1 and Standard Grant Ne/I00646X/1), Japanese Society for the Promotion of Science (JSPS/FF2/60 no. L-11523), NZ Marsden Fund (grant nos. 18-VUW-089 and 15-VUW-131), NSF (grant nos. PLR-1443347 and ACI-1548562), the U.S. Dept. of Energy (grant no. DE-SC0016105), ERC (StG ICEPROXY, 203441; ANR CLIMICE, FP7 Past4Future, 243908), L'Oréal-UNESCO New Zealand For Women in Science Fellowship, University of Otago Research Grant, the IODP U.S. Science Support Program, Spanish Ministry of Science and Innovation (grant no. CTM2017-89711-C2-1-P), and the European Union (FEDER)

Early Spring Phytoplankton Dynamics in the Western Antarctic Peninsula

The Palmer Long-Term Ecological Research program has sampled waters of the western Antarctic Peninsula (wAP) annually each summer since 1990. However, information about the wAP prior to the peak of the phytoplankton bloom in January is sparse. Here we present results from a spring process cruise that sampled the wAP in the early stages of phytoplankton bloom development in 2014. Sea ice concentrations were high on the shelf relative to nonshelf waters, especially toward the south. Macronutrients were high and nonlimiting to phytoplankton growth in both shelf and nonshelf waters, while dissolved iron concentrations were high only on the shelf. Phytoplankton were in good physiological condition throughout the wAP, although biomass on the shelf was uniformly low, presumably because of heavy sea ice cover. In contrast, an early stage phytoplankton bloom was observed beneath variable sea ice cover just seaward of the shelf break. Chlorophyll a concentrations in the bloom reached 2 mg m^(−3) within a 100–150 km band between the SBACC and SACCF. The location of the bloom appeared to be controlled by a balance between enhanced vertical mixing at the position of the two fronts and increased stratification due to melting sea ice between them. Unlike summer, when diatoms overwhelmingly dominate the phytoplankton population of the wAP, the haptophyte Phaeocystis antarctica dominated in spring, although diatoms were common. These results suggest that factors controlling phytoplankton abundance and composition change seasonally and may differentially affect phytoplankton populations as environmental conditions within the wAP region continue to change

Nitrogen Limitation of the Summer Phytoplankton and Heterotrophic Prokaryote Communities in the Chukchi Sea

Major changes to Arctic marine ecosystems have resulted in longer growing seasons with increased phytoplankton production over larger areas. In the Chukchi Sea, the high productivity fuels intense benthic denitrification creating a nitrogen (N) deficit that is transported through the Arctic to the Atlantic Ocean, where it likely fuels N fixation. Given the rapid pace of environmental change and the potentially globally significant N deficit, we conducted experiments aimed at understanding phytoplankton and microbial N utilization in the Chukchi Sea. Ship-board experiments tested the effect of nitrate (NO3-) additions on both phytoplankton and heterotrophic prokaryote abundance, community composition, photophysiology, carbon fixation and NO3- uptake rates. Results support the critical role of NO3- in limiting summer phytoplankton communities to small cells with low production rates. NO3- additions increased particulate concentrations, abundance of large diatoms, and rates of carbon fixation and NO3- uptake by cells >1 μm. Increases in the quantum yield and electron turnover rate of photosystem II in +NO3- treatments suggested that phytoplankton in the ambient dissolved N environment were N starved and unable to build new, or repair damaged, reaction centers. While some increases in heterotrophic prokaryote abundance and production were noted with NO3- amendments, phytoplankton competition or grazers likely dampened these responses. Trends toward a warmer more stratified Chukchi Sea will likely enhance summer oligotrophic conditions and further N starve Chukchi Sea phytoplankton communities

Minimal information for studies of extracellular vesicles 2018 (MISEV2018):a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles (“MISEV”) guidelines for the field in 2014. We now update these “MISEV2014” guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points