Intra-Firm and Inter-Firm Agglomeration: The Location Decisions of Multi-Unit Firms

abstract: Agglomeration research has investigated a key research question, i.e., why do firms in a specific industry co-locate geographically? In the agglomeration literature, it has been assumed that each firm has one business establishment in a cluster such that firms always co-locate with competitors. However, it is often observed that firms operate several business establishments in a cluster, so they co-locate not only with competitors (i.e., inter-firm agglomeration) but also with their own business establishments (i.e., intra-firm agglomeration). While inter-firm agglomeration is a counterpart to the traditional concept of agglomeration, intra-firm agglomeration is a new concept in agglomeration research. The separation between intra-firm and inter-firm agglomeration raises two research questions – 1) how does intra-firm agglomeration differ from inter-firm agglomeration? and 2) do firms decide their locations for intra-firm vs. inter-firm agglomeration differently? These questions actually extend the key question in agglomeration research into a new setting in which firms have several business establishments in a cluster. I proposed that firms can extract more benefits but neutralize more threats from agglomeration through intra-firm agglomeration than through inter-firm agglomeration. I further developed research hypotheses to test this argument in a research context in which multi-unit firms decide their new establishments’ distances to competitors and their other establishments at the same time. The hypotheses received empirical support in an empirical setting in which 10 large multi-unit hotel firms established new hotels in 20 U.S. cities, and several supplementary analyses show that these results are robust.Dissertation/ThesisDoctoral Dissertation Business Administration 201

Characteristics of DMSP-lyase in Phaeocystis sp (Prymnesiophyceae)

The marine phytoplankton species Phaeocystis sp, is one of the few microalgae known to be able to convert dimethylsulfoniopropionate (DMSP) enzymatically into dimethyl sulfide (DMS) and acrylic acid. The function of this enzymatic process for the organism is not known. From experiments with crude extracts and whole cells of axenic cultures of Phaeocystis it was concluded that DMSP-lyase is membrane-bound and located extracellularly because: (1) the enzyme activity in extracts and in whole cells varied in a similar manner with pH; (2) between 50 and 80% of the DMSP-lyase activity was associated with the membrane fraction; (3) lyase activity in whole cells was inhibited by the nonpermeable thiol-reagent p-chloromercuribenzenesulfonic acid (pCMBS). The pH optimum was 10.5 or higher, which is in contrast with available data for the enzyme from other organisms. The pH profile, the requirement for reduced thiol groups in extracts and the inhibition by pCMBS suggest the involvement of cysteine residues at the active site. Production of DMSP as well as its cleavage by DMSP-lyase are apparently not involved in the short term regulation of the osmotic potential of cells upon changes in salinity

Limitation of dimethylsulfoniopropionate synthesis at high irradiance in natural phytoplankton communities of the Tropical Atlantic

Predictions of the ocean-atmosphere flux of dimethyl sulfide will be improved by understanding what controls seasonal and regional variations in dimethylsulfoniopropionate (DMSP) production. To investigate the influence of high levels of irradiance including ultraviolet radiation (UVR), on DMSP synthesis rates (μDMSP) and inorganic carbon fixation (μPOC) by natural phytoplankton communities, nine experiments were carried out at different locations in the low nutrient, high light environment of the northeastern Tropical Atlantic. Rates of μDMSP and μPOC were determined by measuring the incorporation of inorganic 13C into DMSP and particulate organic carbon. Based on measurements over discrete time intervals during the day, a unique μDMSP vs. irradiance (P vs. E) relationship was established. Comparison is made with the P vs. E relationship for μPOC, indicating that light saturation of μDMSP occurs at similar irradiance to μPOC and is closely coupled to carbon fixation on a diel basis. Photoinhibition during the middle of the day was exacerbated by exposure to UVR, causing an additional 55–60% inhibition of both μDMSP and μPOC at the highest light levels. In addition, decreased production of DMSP in response to UVR-induced photoxidative stress, contrasted with the increased net synthesis of photoprotective xanthophyll pigments. Together these results indicate that DMSP production by phytoplankton in the tropical ocean is not regulated in the short term by the necessity to control increasing photooxidative stress as irradiance increases during the day. The study provides new insight into the regulation of resource allocation into this biogeochemically important, multi-functional compatible solute

Annual patterns in phytoplankton phenology in Antarctic coastal waters explained by environmental drivers

Coastal zones of Antarctica harbor rich but highly variable phytoplankton communities. The mechanisms that control the dynamics of these communities are not well defined. Here we elucidate the mechanisms that drive seasonal species succession, based on algal photophysiological characteristics and environmental factors. For this, phytoplankton community structure together with oceanographic parameters was studied over a 5‐year period (2012–2017) at Rothera Station at Ryder Bay (Western Antarctic Peninsula). Algal pigment patterns and photophysiological studies based on fluorescence analyses were combined with data from the Rothera Time‐Series program. Considerable interannual variation was observed, related to variations in wind‐mixing, ice cover and an El Niño event. Clear patterns in the succession of algal classes became manifest when combining the data collected over the five successive years. In spring, autotrophic flagellates with a high light affinity were the first to profit from increasing light and sea ice melt. These algae most likely originated from sea‐ice communities, stressing the role of sea ice as a seeding vector for the spring bloom. Diatoms became dominant towards summer in more stratified and warmer surface waters. These communities displayed significantly lower photoflexibility than spring communities. There are strong indications for mixotrophy in cryptophytes, which would explain much of their apparently random occurrence. Climate models predict continuing retreat of Antarctic sea‐ice during the course of this century. For the near‐future we predict that the marginal sea‐ice zone will still harbor significant communities of haptophytes and chlorophytes, whereas increasing temperatures will mainly be beneficial for diatoms

Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsi shelf during summer

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment

Thin and transient meltwater layers and false bottoms in the Arctic sea ice pack—Recent insights on these historically overlooked features

The rapid melt of snow and sea ice during the Arctic summer provides a significant source of low-salinity meltwater to the surface ocean on the local scale. The accumulation of this meltwater on, under, and around sea ice floes can result in relatively thin meltwater layers in the upper ocean. Due to the small-scale nature of these upper-ocean features, typically on the order of 1 m thick or less, they are rarely detected by standard methods, but are nevertheless pervasive and critically important in Arctic summer. Observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in summer 2020 focused on the evolution of such layers and made significant advancements in understanding their role in the coupled Arctic system. Here we provide a review of thin meltwater layers in the Arctic, with emphasis on the new findings from MOSAiC. Both prior and recent observational datasets indicate an intermittent yet long-lasting (weeks to months) meltwater layer in the upper ocean on the order of 0.1 m to 1.0 m in thickness, with a large spatial range. The presence of meltwater layers impacts the physical system by reducing bottom ice melt and allowing new ice formation via false bottom growth. Collectively, the meltwater layer and false bottoms reduce atmosphere-ocean exchanges of momentum, energy, and material. The impacts on the coupled Arctic system are far-reaching, including acting as a barrier for nutrient and gas exchange and impacting ecosystem diversity and productivity

DMSP synthesis and exudation in phytoplankton:a modeling approach

In the marine environment, phytoplankton are the fundamental producers of dimethylsulfoniopropionate (DMSP), the precursor of the climatically active gas dimethylsulfide (DMS). DMSP is released by exudation, cell autolysis, and zooplankton grazing during phytoplankton blooms. In this study, we developed a model of phytoplankton DMSP and DMS production allowing quantification of the exudation rates of these compounds during different growth phases. The model was tested on published data from axenic cultures of Prorocentrum minimum and Phaeocystis sp.; DMSP exudation rates vary considerably between the 2 species. Model results show that P. minimum exudes around 1% d(-1) of its DMSP quota during the latent, exponential and senescent phases. This is comparable to the average exudation rate estimated from previous laboratory experiments. However, Phaeocystis sp. exudes from 3 to 11% d(-1) of its DMSP quota. For this species, DMSP exudation rates apparently show an inverse relationship with the population growth rate. The maximum DMSP exudation rate in Phaeocystis sp. is 10 times higher than previously reported DMSP or DMS exudation rates. Our results suggest that exudation may be as important as cell autolysis in the release of DMSP during Phaeocystis sp. blooms. We conclude that exudation should be incorporated in models of DMS cycling in the marine environment. Moreover, our results for Phaeocystis sp. suggest that a low and constant exudation rate, as sometimes used in models, is not suitable for all conditions

Pan-Arctic simulation of coupled nutrient-sulfur cycling due to sea ice biology:Preliminary results

A dynamic model is constructed for interactive silicon, nitrogen, sulfur processing in and below Arctic sea ice, by ecosystems residing in the lower few centimeters of the distributed pack. A biogeochemically active bottom layer supporting sources/sinks for the pennate diatoms is appended to thickness categories of a global sea ice code. Nutrients transfer from the ocean mixed layer to drive algal growth, while sulfur metabolites are reinjected from the ice interface. Freeze, flux, flush and melt processes are linked to multielement geocycling for the entire high-latitude regime. Major element kinetics are optimized initially to reproduce chlorophyll observations, which extend across the seasons. Principal influences on biomass are solute exchange velocity at the solid interface, optical averaging in active ice and cell retention against ablation. The sulfur mechanism encompasses open water features such as accumulation of particulate dimethyl sulfoniopropionate, grazing and other disruptive releases, plus bacterial/enzymatic conversion to volatile dimethyl sulfide. For baseline settings, the mixed layer trace gas distribution matches sparging measurements where they are available. However, concentrations rise to well over 10 nM in remote, unsampled locations. Peak contributions are supported by ice grazing, mortality and fractional melting. The model bottom layer adds substantially to a ring maximum of reduced sulfur chemistry that may be dominant across the marginal Arctic environment. Sensitivity tests on this scenario include variation of cell sulfur composition and remineralization, routings/chemical time scales, and the physical dimension of water layers. An alternate possibility that peripheral additions are small cannot be excluded from the outcomes. It is concluded that seagoing dimethyl sulfide data are far too sparse at the present time to distinguish sulfur-ice production levels. Citation: Elliott, S., C. Deal, G. Humphries, E. Hunke, N. Jeffery, M. Jin, M. Levasseur, and J. Stefels (2012), Pan-Arctic simulation of coupled nutrient-sulfur cycling due to sea ice biology: Preliminary results, J. Geophys. Res., 117, G01016, doi:10.1029/2011JG001649