Benthic megafauna assemblage change over three decades in the abyss: Variations from species to functional groups

Megafaunal seafloor assemblages on the Monterey Fan in the NE Pacific (Station M, 4000 m depth) were studied between 2006–2018 using remotely operated vehicles (ROVs) as part of a continuing time-series study that began in 1989. Since 2006 we identified nearly 120,000 individual animals representing over 142 morphospecies, and observed continuous changes in the megafaunal assemblage. This study, which tracked variation in observed morphospecies over a 13-year period, is one of the most detailed long-term records of megafaunal change for abyssal depths. Our investigation shows that new variations continued to emerge, reinforcing the concept that the deep-sea is dynamic over short time scales, rather than static over long periods. Some species were uncommon, but later observed in high numbers, then decreased to very low or undetectable levels (e.g. Elpidia sp. A), while others (e.g. Psychropotes longicauda) exhibited a relatively persistent presence with less fluctuation in abundance. Decreasing total echinoderm density from 2013–2018 did not correspond with the continued occurrence of large episodic POC flux events between 2016–2018. This may be attributed to the quality of food supply arriving at the seafloor and the varied ability of organisms to utilize it. Long-term tracking (30 years) of 10 specific epibenthic echinoderm species originally quantified from camera-sled images shows a pattern of assemblage structure, perhaps returning toward the composition observed in the 1990s and early 2000s. Many questions remain as to how this abyssal site and others will change with continued, and potentially increasing, anthropogenic change in the upper ocean. For example, the marine heat anomaly known as the ‘Warm Blob’ may have influenced major ecological processes at the abyssal seafloor in terms of morphospecies and functional group composition due to changes in POC flux. The degree of dynamism continues to indicate that ad hoc or short-term investigations provide a limited perspective for assessing community structure in conservation or resource exploitation impact assessment studies in the deep sea

Response of deep-sea deposit-feeders to detrital inputs: A comparison of two abyssal time-series sites

Biological communities on the abyssal plain are largely dependent on detritus from the surface ocean as their main source of energy. Seasonal fluctuations in the deposition of that detritus cause temporal variations in the quantity and quality of food available to these communities, altering their structure and the activity of the taxa present. However, direct observations of energy acquisition in relation to detritus availability across megafaunal taxa in abyssal communities are few. We used time-lapse photography and coincident measurement of organic matter flux from water column sediment traps to examine the impact of seasonal detrital inputs on resource acquisition by the deposit feeding megafauna assemblages at two sites: Station M (Northeast Pacific, 4000 m water depth) and the Porcupine Abyssal Plain Sustained Observatory (PAP-SO, Northeast Atlantic 4850 m water depth). At Station M, studied over 18-months, the seasonal particle flux was followed by a salp deposition event. At that site, diversity in types of deposit feeding was related to seabed cover by detritus. At PAP-SO, studied over 30 months, the seasonal particle flux consisted of two peaks annually. While the two study sites were similar in mean flux (~8.0 mgC m−2 d−1), the seasonality in the flux was greater at PAP-SO. The mean overall tracking at PAP-SO was five times that of Station M (1.9 and 0.4 cm2 h−1, respectively); both are likely underestimated because tracking by some common taxa at both sites could not be quantified. At both sites, responses of deposit-feeding megafauna to the input of detritus were not consistent across the taxa studied. The numerically-dominant megafauna (e.g. echinoids, large holothurians and asteroids) did not alter their deposit feeding in relation to the seasonality in detrital supply. Taxa for which deposit feeding occurrence or rate were correlated to seasonality in particle flux were relatively uncommon (e.g. enteropneusta), known to cache food (e.g. echiurans), or to be highly selective for fresh detritus (e.g. the holothurian Oneirophanta mutabilis). Thus, the degree of seasonality in deposit feeding appeared to be taxon-specific and related to natural history characteristics such as feeding and foraging modes

Carbon cycling in the deep eastern North Pacific benthic food web: Investigating the effect of organic carbon input

The deep ocean benthic environment plays a role in long-term carbon sequestration. Understanding carbon cycling in the deep ocean floor is critical to evaluate the impact of changing climate on the oceanic systems. Linear inverse modeling was used to quantify carbon transfer between compartments in the benthic food web at a long time-series study site in the abyssal northeastern Pacific (Station M). Linear inverse food web models were constructed for three separate years in the time-series when particulate organic carbon (POC) flux was relatively high (1990: 0.63 mean mmol C m?2 d?1), intermediate (1995: 0.24) and low (1996: 0.12). Carbon cycling in all years was dominated by the flows involved in the microbial loop; dissolved organic carbon uptake by microbes (0.80–0.95 mean mmol C m?2 d?1), microbial respiration (0.52–0.61), microbial biomass dissolution (0.09–0.18) and the dissolution of refractory detritus (0.46–0.65). Moreover, the magnitude of carbon flows involved in the microbial loop changed in relation to POC input, with a decline in contribution during the high POC influxes, such as those recently experienced at Station M. Results indicate that during high POC episodic pulses the role of faunal mediated carbon cycling would increase. Semi-labile detritus dominates benthic faunal diets and the role of labile detritus declined with increased total POC input. Linear inverse modeling represents an effective framework to analyze high-resolution time-series data and demonstrate the impact of climate change on the deep ocean carbon cycle in a coastal upwelling system

Glass compositions and tempo of post-17 ka eruptions from the Afar Triangle recorded in sediments from lakes Ashenge and Hayk, Ethiopia

AbstractNumerous volcanoes in the Afar Triangle and adjacent Ethiopian Rift Valley have erupted during the Quaternary, depositing volcanic ash (tephra) horizons that have provided crucial chronology for archaeological sites in eastern Africa. However, late Pleistocene and Holocene tephras have hitherto been largely unstudied and the more recent volcanic history of Ethiopia remains poorly constrained. Here, we use sediments from lakes Ashenge and Hayk (Ethiopian Highlands) to construct the first <17 cal ka BP tephrostratigraphy for the Afar Triangle. The tephra record reveals 21 visible and crypto-tephra layers, and our new database of major and trace element glass compositions will aid the future identification of these tephra layers from proximal to distal locations. Tephra compositions include comendites, pantellerites and minor peraluminous and metaluminous rhyolites. Variable and distinct glass compositions of the tephra layers indicate they may have been erupted from as many as seven volcanoes, most likely located in the Afar Triangle. Between 15.3−1.6 cal. ka BP, explosive eruptions occurred at a return period of <1000 years. The majority of tephras are dated at 7.5−1.6 cal. ka BP, possibly reflecting a peak in regional volcanic activity. These findings demonstrate the potential and necessity for further study to construct a comprehensive tephra framework. Such tephrostratigraphic work will support the understanding of volcanic hazards in this rapidly developing region

Reprint of Glass compositions and tempo of post-17 ka eruptions from the Afar Triangle recorded in sediments from lakes Ashenge and Hayk, Ethiopia

Numerous volcanoes in the Afar Triangle and adjacent Ethiopian Rift Valley have erupted during the Quaternary, depositing volcanic ash (tephra) horizons that have provided crucial chronology for archaeological sites in eastern Africa. However, late Pleistocene and Holocene tephras have hitherto been largely unstudied and the more recent volcanic history of Ethiopia remains poorly constrained. Here, we use sediments from lakes Ashenge and Hayk (Ethiopian Highlands) to construct the first <17 cal ka BP tephrostratigraphy for the Afar Triangle. The tephra record reveals 21 visible and crypto-tephra layers, and our new database of major and trace element glass compositions will aid the future identification of these tephra layers from proximal to distal locations. Tephra compositions include comendites, pantellerites and minor peraluminous and metaluminous rhyolites. Variable and distinct glass compositions of the tephra layers indicate they may have been erupted from as many as seven volcanoes, most likely located in the Afar Triangle. Between 15.3?1.6 cal. ka BP, explosive eruptions occurred at a return period of <1000 years. The majority of tephras are dated at 7.5?1.6 cal. ka BP, possibly reflecting a peak in regional volcanic activity. These findings demonstrate the potential and necessity for further study to construct a comprehensive tephra framework. Such tephrostratigraphic work will support the understanding of volcanic hazards in this rapidly developing regionpublishersversionPeer reviewe

Episodic organic carbon fluxes from surface ocean to abyssal depths during long-term monitoring in NE Pacific

Growing evidence suggests substantial quantities of particulate organic carbon (POC) produced in surface waters reach abyssal depths within days during episodic flux events. A 29-year record of in situ observations was used to examine episodic peaks in POC fluxes and sediment community oxygen consumption (SCOC) at Station M (NE Pacific, 4,000-m depth). From 1989 to 2017, 19% of POC flux at 3,400 m arrived during high-magnitude episodic events (≥mean + 2 σ), and 43% from 2011 to 2017. From 2011 to 2017, when high-resolution SCOC data were available, time lags between changes in satellite-estimated export flux (EF), POC flux, and SCOC on the sea floor varied between six flux events from 0 to 70 days, suggesting variable remineralization rates and/or particle sinking speeds. Half of POC flux pulse events correlated with prior increases in EF and/or subsequent SCOC increases. Peaks in EF overlying Station M frequently translated to changes in POC flux at abyssal depths. A power-law model (Martin curve) was used to estimate abyssal fluxes from EF and midwater temperature variation. While the background POC flux at 3,400-m depth was described well by the model, the episodic events were significantly underestimated by ∼80% and total flux by almost 50%. Quantifying episodic pulses of organic carbon into the deep sea is critical in modeling the depth and intensity of POC sequestration and understanding the global carbon cycle

Recurrent explosive eruptions from a high risk Main Ethiopian Rift volcano throughout the Holocene

Corbetti caldera is the southernmost large volcanic system in Ethiopia, and has been categorized at the highest level of uncertainty in terms of hazard and risk. Until now, the number and frequency of past explosive eruptions at Corbetti has been unknown, due to limited studies of frequently incomplete and patchy outcrop sequences. Here we use volcanic ash layers preserved in sediments from three Main Ethiopian Rift lakes to provide the first detailed record of volcanism for the Corbetti caldera. We show that lake sediments yield more comprehensive, stratigraphically-resolved dossiers of long-term volcanism than often available in outcrop. Our eruptive history for Corbetti spans the last 10 k.y. and reveals eruptions at an average return period of ~900 years. The threat posed by Corbetti has, until now, been underestimated. Future explosive eruptions, similar to those of the past 10 k.y. would blanket nearby Awassa and Shashamene, currently home to ~260,000 people, with pumice fall deposits and would have significant societal impacts. A lake sediment tephrostratigraphic approach shows significant potential for application throughout the East African Rift system, and will be essential to better understanding volcanic hazards in this rapidly developing region.</p

Identification and cardiotropic actions of sulfakinin peptides in the American lobster Homarus americanus

In arthropods, a group of peptides possessing a -Y(SO3H)GHM/ LRFamide carboxy-terminal motif have been collectively termed the sulfakinins. Sulfakinin isoforms have been identified from numerous insect species. In contrast, members of this peptide family have thus far been isolated from just two crustaceans, the penaeid shrimp Penaeus monodon and Litopenaeus vannamei. Here, we report the identification of a cDNA encoding prepro-sulfakinin from the American lobster Homarus americanus. Two sulfakinin-like sequences were identified within the open-reading frame of the cDNA. Based on modifications predicted by peptide modeling programs, and on homology to the known isoforms of sulfakinin, particularly those from shrimp, the mature H. americanus sulfakinins were hypothesized to be pEFDEY(SO3H)GHMRFamide (Hoa-SK I) and GGGEY(SO3H)DDY(SO3H)GHLRFamide (Hoa-SK II). Hoa-SK I is identical to one of the previously identified shrimp sulfakinins, while Hoa-SK II is a novel isoform. Exogenous application of either synthetic Hoa-SK I or Hoa-SK II to the isolated lobster heart increased both the frequency and amplitude of spontaneous heart contractions. In preparations in which spontaneous contractions were irregular, both peptides increased the regularity of the heartbeat. Our study provides the first molecular characterization of a sulfakinin-encoding cDNA from a crustacean, as well as the first demonstration of bioactivity for native sulfakinins in this group of arthropods

Supporting Advocacy, Deliberation, and Civic Learning in the Classroom

We live, teach and learn in complicated times. As faculty in higher education, we have the opportunity to help uphold the civic purpose of higher education. We are accustomed to helping students navigate academic information, and to equipping them for more standard academic tasks. Through thoughtful course design, we can also help our students become better consumers and evaluators of less traditionally academic information: from critically interpreting what they read and see in the news media, to engaging the arguments of their friends, peers and family members. Further, we can challenge our students to use these evaluative skills to engage in debate and advocacy activities around critical issues of the day

JINGLE V: Dust properties of nearby galaxies derived from hierarchical Bayesian SED fitting

We study the dust properties of 192 nearby galaxies from the JINGLE survey using photometric data in the 22-850μm range. We derive the total dust mass, temperature T and emissivity index β of the galaxies through the fitting of their spectral energy distribution (SED) using a single modified black-body model (SMBB). We apply a hierarchical Bayesian approach that reduces the known degeneracy between T and β. Applying the hierarchical approach, the strength of the T-β anti-correlation is reduced from a Pearson correlation coefficient R = -0.79 to R = -0.52. For the JINGLE galaxies we measure dust temperatures in the range 17 - 30 K and dust emissivity indices β in the range 0.6 - 2.2. We compare the SMBB model with the broken emissivity modified black-body (BMBB) and the two modified black-bodies (TMBB) models. The results derived with the SMBB and TMBB are in good agreement, thus applying the SMBB, which comes with fewer free parameters, does not penalize the measurement of the cold dust properties in the JINGLE sample. We investigate the relation between T and β and other global galaxy properties in the JINGLE and Herschel Reference Survey (HRS) sample. We find that β correlates with the stellar mass surface density (R = 0.62) and anti-correlates with the HI mass fraction (MHI/M*, R = -0.65), whereas the dust temperature correlates strongly with the SFR normalized by the dust mass (R = 0.73). These relations can be used to estimate T and β in galaxies with insufficient photometric data available to measure them directly through SED fitting