514 research outputs found
Joe Hickman
No full textJoe Hickman, shown here at Fruita, Utah, was the great grandson of the notorious Bill Hickman. Bill Hickman (1815-1883) was an early Mormon pioneer settler, lawman, and legislator, who later became an excommunicated author, murderer, and outlaw
Dez Hickman
No full textDez Hickman, milking a cow at Torrey, Utah, was a Great Grandson of the notorious Bill Hickman. Bill Hickman (1815-1883) was an early Mormon pioneer settler, lawman, and legislator, who later became an excommunicated author, murderer, and outlaw
Bill Hickman
No full textThis picture of Bill Hickman and his signature appear on the cover of his book, BRIGHAM\u27S DESTROYING ANGEL, published by Shepherd Publishing Company in 1904. Bill Hickman (1815-1883) was an early Mormon pioneer settler, lawman, and legislator, who later became an excommunicated author, murderer, and outlaw
Bill Hickman
No full textBill Hickman (1815-1883) was an early Mormon pioneer settler, lawman, and legislator, who later became an excommunicated author, murderer, and outlaw
The photophysiology and primary productivity of phytoplankton within the deep chlorophyll maximum
No full textIn temperate shelf seas, a deep chlorophyll maximum (DCM) persists within the thermocline during summer stratification. This study explores the significance of primary production (PP) within the DCM and provides a detailed investigation into the mechanisms of phytoplankton adaptation to this tidally dynamic and dimly-lit environment. Comparison is drawn to the DCM in a range of hydrographic regimes in the open ocean. Data are presented from two cruises in the Celtic Sea during summer (2003 and 2005) and one from the Atlantic Ocean (AMT15, 2004). Phytoplankton physiological measurements were obtained from 14C Photosynthesis vs. Irradiance (P vs. E) experiments and a bench-top Fast Repetition Rate Fluorometer (FRRF). Water-column profiles of PP were empirically modelled using P vs. E parameters and measurements of spectral in situ irradiance.Across the Celtic Sea shelf the DCM was located towards the base of the thermocline and was tightly coupled to the nitracline. The thermocline is presented as a 3-layer system, the top and bottom layers dominated by physical mixing and a mid-layer which is relatively stable and occurs at the top of the nitracline. Nitrate flux into the thermocline from the BML was maximal at spring tides and could support almost all the PP in the thermocline. It appears that nitrate supply and utilisation is roughly balanced over spring - neap timescales.Within the shelf sea thermocline, layering of phytoplankton taxonomy was observed, with the maxima of cell concentrations decoupled from those of cellular pigment concentrations. The FRRF-derived effective absorption cross section of photosystem II (?PSII) and photosynthetic efficiency (Fv/Fm) co-varied with pigment composition, and did not appear to contribute to photo-acclimation. Data indicated that the mechanism of photo-acclimation was by the number, rather than size, of PSII reaction centres.In contrast to the surface mixed layer, phytoplankton at the DCM remained light limited and PP in the thermocline was more sensitive to incident irradiance than in the surface. In the Celtic Sea, the potential range in water-column integrated PP between a cloudy and sunny day was greater than the spatial range in PP across the region. PP within the thermocline contributed 28 – 84 % of vertically-integrated daily PP.The mechanism of photoacclimation appeared to be consistent between the shelf sea and open ocean environments. Throughout the Atlantic Ocean PP in the DCM contributed between 15 – 80 % of total water column production.It is shown that physical – biological coupling is a major determinant on phytoplankton taxonomy, physiology and productivity in the DCM
Ocean colour signature of climate change
No full textMonitoring changes in marine phytoplankton is important as they form the foundation of the marine food web and are crucial in the carbon cycle. Often Chlorophyll-a (Chl-a) is used to track changes in phytoplankton, since there are global, regular satellite-derived estimates. However, satellite sensors do not measure Chl-a directly. Instead, Chl-a is estimated from remote sensing reflectance (RRS): the ratio of upwelling radiance to the downwelling irradiance at the ocean’s surface. Using a model, we show that RRS in the blue-green spectrum is likely to have a stronger and earlier climate-change-driven signal than Chl-a. This is because RRS has lower natural variability and integrates not only changes to in-water Chl-a, but also alterations in other optically important constituents. Phytoplankton community structure, which strongly affects ocean optics, is likely to show one of the clearest and most rapid signatures of changes to the base of the marine ecosystem
Assessing the potential of backscattering as a proxy for phytoplankton carbon biomass
No full textDespite phytoplankton contributing roughly half of the photosynthesis on earth and fueling marine food-webs, field measurements of phytoplankton biomass remain scarce. The particulate backscattering coefficient (b
bp ) has often been used as an optical proxy to estimate phytoplankton carbon biomass (C
phyto ). However, total observed b
bp is impacted by phytoplankton size, cell composition, and non-algal particles. The lack of phytoplankton field data has prevented the quantification of uncertainties driven by these factors. Here, we first review and discuss existing b
bp algorithms by applying them to b
bp data from the BGC-Argo array in surface waters (<10 m). We find a b
bp threshold where estimated C
phyto differs by more than an order of magnitude. Next, we use a global ocean circulation model (the MITgcm Biogeochemical and Optical model) that simulates plankton dynamics and associated inherent optical properties to quantify and understand uncertainties from b
bp-based algorithms in surface waters. We do so by developing and calibrating an algorithm to the model. Simulated error-estimations show that b
bp-based algorithms overestimate/underestimate C
phyto between 5% and 100% in surface waters, depending on the location and time. This is achieved in the ideal scenario where C
phyto and b
bp are known precisely. This is not the case for algorithms derived from observations, where the largest source of uncertainty is the scarcity of phytoplankton biomass data and related methodological inconsistencies. If these other uncertainties are reduced, the model shows that b
bp could be a relatively good proxy for phytoplankton carbon biomass, with errors close to 20% in most regions.</p
Shelf sea subsurface chlorophyll maximum thin layers have a distinct phytoplankton community structure
No full textThe Western English Channel is a seasonally stratified temperate coastal sea where a subsurface chlorophyll maximum (SCM) is typically detectable within the seasonal thermocline. The SCM often develops as a thin layer(<5m) that may contain elevated concentrations of phytoplankton (subsurface chlorophyll maximum thin layer;SCMTL). During summer 2013 a study was conducted offshore of Falmouth, UK to assess spatial and short-termtemporal variability in SCM thickness in relation to water column structure and physical conditions and to evaluateany associated changes in phytoplankton community structure. SCMTL were observed in 18 of 52 verticalprofiles, typically characterised by higher chlorophyll concentrations than broader SCM. SCMTL were generallyassociated with a ‘stepped’ thermocline, likely representing the presence of one or more shallow mixed layersforming above/within the seasonal thermocline, and related to increased stratification and stability compared tobroader SCM. Pseudo-nitzschia was almost exclusively the dominant diatom taxon in SCM, yet statistically distinctdifferences in community structure existed between SCMTL and broader SCM. Within the phytoplankton,the distinction was largely due to a greater biomass of Proboscia alata and other rhizosolenid diatoms, and thedinoflagellate Ceratium lineatum in SCMTL, and a smaller population of the diatom Chaetoceros spp. There wasalso a distinction amongst heterotrophic dinoflagellates, with enhanced biomass of Gyrodinium spp. in SCMTLand a reduction in Diplopsalis lenticula. We propose that this observed difference resulted from promotion of phytoplanktonbetter adapted to environmental conditions more specific to SCMTL compared to broader SCM. Withmore intense and prolonged stratification projected for the NW European shelf, there may be increased prevalenceof SCMTL and the associated larger-sized specialised taxa, with implications for increased carbon export.This study adds to a growing body of evidence of the importance of SCMTL in coastal and shelf seas, and highlightsthe requirement for improved understanding of physical forcing, and the ecology and physiology of keytaxa, particularly as predicted changes in stratification could alter the role of SCM phytoplankton in a future influencedby climate chang
Dragmacidon hendersoni Sim-Smith & Hickman & Kelly 2021, sp. nov.
No full textDragmacidon hendersoni sp. nov. (Fig. 13) Material examined. Holotype — MCCRDS9412, Nameless Island, 0.670° S, 90.586° W, 9 m, 9 Aug 2003. Type locality. Nameless Island; 9 m. Habitat and distribution. Only known from the type locality. Found in a recess on a vertical wall growing on rock; 9 m. Description. Thinly encrusting sponge, 3 mm thick, with a minutely ridged and punctate surface. A few small oscules are scattered over the surface of the sponge. Texture is compressible, surface is faintly hispid. Colour in life is bright yellow, colour in ethanol is tan (Fig. 13A). Skeleton. Choanosomal skeleton is loosely plumoreticulate, with delicate, multispicular primary tracts and vague secondary tracts/connections. Bundles of styles protrude through the surface of the sponge, in tufts, points uppermost. There is no special ectosome (Fig. 13B). Spicules. Megascleres— Style I (Fig. 13C), small, slender and slightly curved; 231 (209–248) × 6 (4–7) µm (n = 20). Style II (Fig. 13D), very slender and often strongly curved or slightly sinuous; 197 (127–334) × 2.4 (1.2–3.4) µm (n = 20). Etymology. Named after Scott Henderson, who accompanied co-author Cleveland Hickman on numerous trips to the Galápagos from 1983–2016. He assisted Cleve in a variety of roles from local negotiator and logistics organiser, divemaster during harrowing high-current dives, trusted friend and host on his Santa Cruz coffee farm. Of the 149 students Cleve led on 12 Galápagos student field trips, Scott was the only one to make Galápagos his home and life-long conservation project. Remarks. Dragmacidon hendersoni sp. nov. differs considerably from D. raeae sp. nov. by: live colouration (yellow vs bright red); skeleton (compact plumoreticulate vs loosely plumoreticulate to plumose); texture (firm vs compressible); and the possession of two size categories of styles, with both categories being more slender and sinuous than those of D. raeae sp. nov. It also differs considerably from the previously recorded D. oxeon which has much longer megascleres. It differs from all other tropical/subtropical eastern Pacific species by the lack of oxeas. Table 4 provides useful details on all known species of Dragmacidon, many of which appear to fall loosely into two groups: those that were previously identified as species of Pseudaxinella Schmidt, 1875 [D. raeae sp. nov. and other species that form firm dome-shaped sponges, with compact plumoreticulate skeletons that often lack trichodragmata, such as D. australe (Bergquist, 1970), D. coccineum (Keller, 1891), D. debitusae (Hooper & Lévi, 1993)]; and those that have a looser, more plumose skeleton with longer, more sinuous megascleres and often raphides in trichodragmata, resulting in a softer, less firm sponge, such as D. oxeon, D. mutans (Sarà, 1978), D. tumidum (Dendy, 1897), and D. decipiens (Wiedenmayer, 1989). The addition of two species from the Galápagos Archipelago, each of which falls loosely into one or the other group, may lend additional data for future detailed analysis of Dragmacidon, a genus of convenience into which all species commonly previously recorded as Pseudaxinella (a junior synonym of Axinella), were assigned by Alvarez & Hooper (2002: 734).Published as part of Sim-Smith, Carina, Hickman, Cleveland & Kelly, Michelle, 2021, New shallow-water sponges (Porifera) from the Galápagos Islands, pp. 1-71 in Zootaxa 5012 (1) on pages 30-31, DOI: 10.11646/zootaxa.5012.1.1, http://zenodo.org/record/515806
Constraining the response of phytoplankton to zooplankton grazing and photo-acclimation in a temperate shelf sea with a 1-D model - towards S2P3 v8.0
No full textAn established 1-dimensional model of Shelf Sea Physics and Primary Production (S2P3) has been developed into three different new models: S2P3-NPZ which includes a Nutrient-Phytoplankton-Zooplankton (NPZ) framework, where the grazing rate is no longer fixed, but instead varies over time depending on different functions chosen to represent the predator- prey relationship between zooplankton and phytoplankton; S2P3-Photoacclim which includes a representation of the process of photo-acclimation and flexible stoichiometry in phytoplankton; and S2P3 v8.0 which combines the NPZ framework and the variable stoichiometry of phytoplankton at the same time. These model formulations are compared to buoy and CTD observations, as well as zooplankton biomass and in situ phytoplankton physiological parameters obtained in the Central Celtic Sea (CCS). Models were calibrated by comparison to observations of the timing and magnitude of the spring phytoplankton bloom, magnitude of the spring zooplankton bloom, and phytoplankton physiological parameters obtained throughout the water column. A sensitivity study was also performed for each model to understand the effects of individual parameters on model dynamics. Results demonstrate that better agreement with biological observations can be obtained through the addition of representations of photo-acclimation, flexible stoichiometry, and grazing provided these can be adequately constrained.</p
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