Nutrient Mass Flux between Florida Bay and the Florida Keys National Marine Sanctuary

There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year^?1 and 63 (±7) ton P year^?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs.     

Regions and sustainable development: regional planning matters

This paper looks at how the term 'sustainable development' has been used in the process of regional plan making over the past decade. It emphasizes the differing geographies of these debates within England, in terms of how sustainable development has been used to justify different types of approach in different parts of the country. Both drawing on and challenging recent work on state theory, the paper argues the need to see regional planning as a part of a multi-scalar governance system, whose importance should not be underestimated.     

基于开放互操作标准的分布式地理空间模型共享研究

传统的单机环境和封闭式网络环境由于有限的资源利用能力, 难以充分支持分散地学数据、模型等资源的共享与应用集成。基于网络环境的信息交换特点, 提出了分布式地理空间模型共享的服务体系。该体系以数据、模型、元数据等互操作要素为核心, 通过网络将数据、模型等网络节点进行开放式耦合。针对地理空间模型服务的互操作问题, 提出了分布式环境下的模型共享服务交互接口, 该接口定义了模型服务元数据、模型服务的交互操作、模型服务的通讯方式等交互规则, 尽可能地降低模型服务与模型终端之间在数据交换、功能调用等方面的互操作困难。为了降低将模型共享为模型服务的实现难度, 设计和开发了地理空间模型共享平台, 并介绍了在该平台上发布地理空间模型的2种方法。最后介绍了研究成果在Prairie生态模型共享方面的应用实践。     

Tidal and low-frequency net displacement in a coastal lagoon

Four, 32-day current meter records from the Indian River lagoon, Florida, are used to characterize flow patterns along the Intracoastal Waterway in a coastal lagoon. The M₂ tidal constituent amplitude decreases from 58 cm per s near the Fort Pierce Inlet to only 7 cm per s in the interior of the lagoon. The relative importance of the nontidal variance in the current meter records increases from 0.6% to 26.6% of the total over the same distance. Plots of net displacement over time intervals of one to 16 days suggest relatively rapid flushing near the inlet, but in the interior of the lagoon periods of little or no net movement are increasingly common. Low-frequency motions at all four sites are coherent with windstress over time scales in excess of approximately two days.     

Contained turbidites used to track sea bed deformation and basin migration, Sorbas Basin, south-east Spain

ABSTRACT The mechanisms driving subsidence in late orogenic basins are often not easily resolved on account of later fault reactivation and a rapidly changing stress field. Contained turbidites in such basins provide a unique opportunity of monitoring sea bed deformation and evolving bathymetry and hence patterns of subsidence during basin filling. A variety of interpretations have been proposed to explain subsidence in Neogene basins in SE Spain, including extensional, strike‐slip and thrust top mechanisms. Ponded turbidite sheets on the floor of the Neogene Sorbas Basin (SE Spain) were deposited by sand‐bearing currents which ran into enclosed bathymetric deeps where they underwent rapid suspension collapse. The structure and distribution of these sheets (and the thick mudstone caps which overlie them) act as a proxy for the containing sea bed bathymetry at the time of deposition. An analysis of the sheet architecture helps identify a trough‐axial zone of syndepositional faulting and reveals a westwards stepping of the ponding depocentre with time. Fault breaks at the sea bed influenced the position of flow arrest and the distribution of sandstone beds on the basin floor. Westward stepping of the deeper bathymetry was episodic and probably controlled by transverse faults. Re‐locations of the depocentre were accompanied by the destabilization of carbonate sand stores on the margins of the basin, resulting in the repeated emplacement of large‐volume carbonate megabeds and calciturbidites. The fill to the Sorbas Basin was shingled by the onset of compression in the east attributed to transfer of slip between intersecting strike‐slip fault strands. A sinistral fault (a splay of the Carboneras Fault System) propagated through the evolving basin fill from the east as the eastern part of the basin became inverted and the locus of subsidence migrated into the Tabernas area 20 km area to the west. The sedimentological analysis of the basin fill helps see through a late dextral overprint which ultimately juxtaposed basement rocks to the south against the inverted and upended basin, along a late slip‐modified unconformity. Conventional palaeostress analysis of fractures along the basin margin fails to see past this late dextral shearing event. Basin migration parallel to the E–W‐orientated basin axis, slip‐reversal (sinistral to dextral) and the active involvement of strike‐slip faults are now identified as important aspects of the evolution of the Sorbas Basin during the latestTortonian.     

The rise and fall of the estuarine intertidal zone

Water level records from two study sites in Indian River Lagoon, along Florida’s Atlantic Coast, are used to characterize the vertical displacement of the estuarine intertidal zone in response to subtidal frequency forcing. A 22-year water level record indicates that the seasonal cycle has a range approximately one-quarter greater than the mean tidal range. The intertidal zone thus rises and falls to such an extent that over time scales in excess of several weeks there is no layer which consistently experiences an alternating exposure and inundation. Six-year sets of high and low tide extremes from the second study site are expressed in the form of cummulative histograms to determine the probabilities with which high tide and low tide levels lying outside of median values will occur in response to the interaction of tidal constituents and low-frequency forcing. High and low water values are then stratified by month, and probability distributions are recomputed for each subset. In this study area, unpredictable, low-frequency water level fluctuations perturb the intertidal zone to such an extent that the probabilities of extreme high and low water levels, in addition to mean high and low water, must be determined to characterize the stuarine intertidal zone adequately. *** DIRECT SUPPORT *** A01BY034 00002     

'Linked' debrites in sand-rich turbidite systems – origin and significance

Abstract The outer parts of a number of small Late Jurassic sandy deep‐water fans in the northern North Sea are dominated by the stacked deposits of co‐genetic sandy and muddy gravity flows. Sharp‐based, structureless and dewatered sandstone beds are directly overlain by mudclast breccias that are often rich in terrestrial plant fragments and capped by thin laminated sandstones, pseudonodular siltstones and mudstones. The contacts between the clast‐rich breccias and the underlying sandstones are typically highly irregular with evidence for liquefaction and upward sand injection. The breccias contain fragments (up to metre scale) of exotic lithologies surrounded by a matrix that is extremely heterogeneous and strewn with multiphase and variably sheared sand injections and scattered coarse and very coarse sand grains (often coarser than in the immediately underlying sand bed). Markov chain analysis establishes that the breccias consistently overlie sandstones, and the character of the breccias and their external contacts rule out a post‐depositional origin via in situ liquefaction, intrastratal flowage or bed amalgamation and disruption. The breccias are interpreted as debrites that rode on a water‐rich sand bed just deposited by a co‐genetic concentrated gravity current. As such, they are referred to as ‘linked debrites’ to distinguish them from debrites emplaced in the absence of a precursor sand bed. The distinction is important, because these linked debris flows can achieve significant mobility through entrainment of both water and sediment from beneath, and they ride on a low‐friction carpet of liquefied sand. This explains the paradox presented by fan fringes in which there are common debrites, when conventional thinking might predict that deposits of low‐concentration gravity currents should be more important here. In fact, evidence for transport by low‐concentration turbidity currents is rare in these systems. Several possible mechanisms might explain the formation of linked flows, but the ultimate source of both sandy and clast‐rich flow components must be in shallower water on the basin margin (the debrites are not triggered from distal slopes). Flow partitioning may have occurred by upslope erosion and retardation of the mudclast‐charged portion of an erosional sandy density current, partial flow transformation of a precursor debris flow and/or hydraulic segregation and reconcentration of the flaky clasts and carbonaceous matter during transport. Linked debrites are not restricted to small sand‐rich fans, and similar mechanisms may be responsible for the long runout of debris flows in other systems. The recognition of a distinct class of linked debrites is of wider importance for facies prediction, reservoir heterogeneity and even carbon fluxes and sequestration on continental margins.     

Flow dynamics over a foredune scarp

The nature of wind flow over a small, 0.6 m high foredune scarp is investigated on the Sir Richard Peninsula, South Australia during a variety of incident wind directions and speeds. The study provides additional supporting evidence that the presence of the scarp and the dune exerts a strong influence on a landwards trending reduction in wind velocity and an increase in turbulence, with the greatest area of turbulence occurring near and at the foredune scarp base. For an incident oblique wind, an alongshore helicoidal flow is formed within a separation region along the scarp basal region. In this region, the coefficient of variation (CV) of wind speed is high and displays significant fluctuations. The flow at the scarp crest is compressed, streamlined and accelerated, turbulence is suppressed, and local jets may occur depending on the incident wind approach angle. Jets are more likely where the incident flow is perpendicular or nearly so. A flow separation region does not develop downwind of the scarp crest where the morphology of the foredune stoss slope downwind of the scarp is more convex (as in this case) rather than relatively flat, and possibly due to the presence of vegetation at the scarp crest. A tentative model of the flow regions developed across a backshore–scarp–foredune region during oblique incident flow is provided. © 2018 John Wiley & Sons, Ltd.     

Hybrid sediment gravity flow deposits – Classification, origin and significance

The deposits of subaqueous sediment gravity flows can show evidence for abrupt and/or progressive changes in flow behaviour making them hard to ascribe to a single flow type (e.g. turbidity currents, debris flows). Those showing evidence for transformation from poorly cohesive and essentially turbulent flows to increasingly cohesive deposition with suppressed turbulence ‘at a point’ are particularly common. They are here grouped as hybrid sediment gravity flow deposits and are recognised as key components in the lateral and distal reaches of many deep-water fan and basin plain sheet systems. Hybrid event beds contain up to five internal divisions: argillaceous and commonly mud clast-bearing sandstones (linked debrite, H3) overlie either banded sandstones (transitional flow deposits, H2) and/or structureless sandstones (high-density turbidity currents, H1), recording longitudinal and/or lateral heterogeneity in flow structure and the development of turbulent, transitional and laminar flow behaviour in different parts of the same flow. Many hybrid event beds are capped by a relatively thin, well-structured and graded sand–mud couplet (trailing low-density turbulent cloud H4 and mud suspension fallout H5). Progressive bed aggradation results in the deposits of the different flow components stacked vertically in the final bed. Variable vertical bed character is related to the style of up-dip flow transformations, the distance over which the flows can evolve and partition into rheological distinct sections, the extent to which different flow components mutually interact, and the rate at which the flows decelerate, reflecting position (lateral versus distal) and gradient changes. Hybrid beds may inherit their structure from the original failure, with turbidity currents outpacing debris flows from which they formed via partial flow transformation. Alternatively, they may form where sand-bearing turbidity currents erode sufficient substrate to force transformation of a section of the current to form a linked debris flow. The incorporation of mud clasts, their segregation in near-bed layers and their disintegration to produce clays that can dampen turbulence are inferred to be key steps in the generation of many hybrid flow deposits. The occurrence of such beds may therefore identify the presence of non-equilibrium slopes up-dip that were steep enough to promote significant flow incision. Where hybrid event beds dominate the entire distal fan stratigraphy, this implies either the system was continually out of grade in order to freight the flows with mud clasts and clays, or the failure mechanism and transport path repeatedly allowed transmission of components of the initial slumps distally. Where hybrid beds are restricted to sections representing fan initiation, or occur more sporadically within the fan deposits, this could indicate shorter episodes of disequilibrium, due to an initial phase of slope re-adjustment, or intermittent tectonically or gravity-driven surface deformation or supply variations. Alternatively, changes between conventional and hybrid event beds may record changes in the flow generation mechanism through time. Thus the vertical distribution of hybrid event beds may be diagnostic of the wider evolution of the fan systems that host them.     

The influence of wind forcing on across-shelf transport in the Florida Keys

Acoustic Doppler current profiles and current meter data are combined with wind observations to describe the transport of water leaving Florida Bay and moving onto the inner shelf on the Atlantic side of the Florida Keys. A 275-day study in the Long Key Channel reveals strong tidal exchanges, but the average ebb tide volume leaving Florida Bay is 19% greater than the average flood tide volume entering the bay. The long-term net outflow averages 472 m³ s⁻¹. Two studies in shelf waters describe the response to wind forcing during spring and summer months in 2004 and during fall and winter months in 2004–2005. During the spring–summer study, southeasterly winds have a distinct shoreward component, and a two-layer pattern appears. Surface layers move shoreward while near-bottom layers move seaward. During the winter study, the resultant wind direction is parallel to the Keys and to the local isobaths. The entire water column moves in a nearly downwind direction, and across-shelf transport is relatively small. During the summer wet season, Florida Bay water should be warmer, fresher, and thus less dense than Atlantic shelf waters. Ebbing bay water should move onto the shelf as a buoyant plume and be held close to the Keys by southeasterly winds. During the winter dry season, colder and saltier Florida Bay water should leave the tidal channels with relatively high density and be concentrated in the near-bottom layers. But little across-shelf flow occurs with northeasterly winds. The study suggests that seasonally changing wind forcing and hydrographic conditions serve to insulate the reef tract from the impact of low-quality bay water.