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.     

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.     

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     

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.     

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.     

On the generation of climate model ensembles

Climate model ensembles are used to estimate uncertainty in future projections, typically by interpreting the ensemble distribution for a particular variable probabilistically. There are, however, different ways to produce climate model ensembles that yield different results, and therefore different probabilities for a future change in a variable. Perhaps equally importantly, there are different approaches to interpreting the ensemble distribution that lead to different conclusions. Here we use a reduced-resolution climate system model to compare three common ways to generate ensembles: initial conditions perturbation, physical parameter perturbation, and structural changes. Despite these three approaches conceptually representing very different categories of uncertainty within a modelling system, when comparing simulations to observations of surface air temperature they can be very difficult to separate. Using the twentieth century CMIP5 ensemble for comparison, we show that initial conditions ensembles, in theory representing internal variability, significantly underestimate observed variance. Structural ensembles, perhaps less surprisingly, exhibit over-dispersion in simulated variance. We argue that future climate model ensembles may need to include parameter or structural perturbation members in addition to perturbed initial conditions members to ensure that they sample uncertainty due to internal variability more completely. We note that where ensembles are over- or under-dispersive, such as for the CMIP5 ensemble, estimates of uncertainty need to be treated with care.     

Longitudinal transport in a coastal lagoon

A two-dimensional, finite difference numerical model is used to describe longitudinal transport through a transverse cross section into and out of the northern segment of Indian River lagoon, along the Atlantic coast of Florida. The model uses four layers to represent the Atlantic Intracoastal Waterway, and two layers in the shallow waters east and west of the waterway to quantify transport. Simulations during a 161-day period from late June through late November 1983 include a seasonal shift in the longitudinal component of the wind. Transport is in the same sense throughout the cross section 32% of the time. Relatively subtle lateral shear, however, has a profound effect on long-term net transport. For most of the study, cumulative net transport in the shallow areas on either side of the waterway follows the cumulative along-channel windstress, but it is directed upwind in the lower half of the Intracoastal Waterway. Four numerical experiments examine the relative importance of terms in the momentum equation and components of the database. Results suggest that time-varying baroclinic forcing is an important component of the pressure gradient. Simulations which ignore water-level variations at the open end of the model differ substantially from those which incorporate water-level fluctuations.