On the upwelling circulation over the wide shelf off Peru: 1. Circulation

During November-December 1977, a modest physical field experiment was carried out over the wide shelf off northern Peru near 9S. Repeated sections of temperature and absolute current profiles were run along two lines with 60 km alongshore separation. Local winds were moderate, rather uniform and favorable for upwelling throughout the study period...

On the upwelling circulation over the wide shelf off Peru: 2. Vertical velocities, internal mixing and heat balance

An analysis is presented of the mean coastal upwelling circulation over the wide shelf off Peru based on the current and temperature profiling measurements described in Shaffer (1982). The natural coordinate conservation method (NCCM) in temperature (T) space is applied to boxes formed from stations along two lines with 60 km alongshore separation. Mean distributions in x (cross-shelf coordinate) and T are obtained for diapycnal advection and mixing. The vertical component of isopycnal flow is also calculated and found to be considerably less than vertical, diapycnal flow in this region of strong upwelling and internal mixing.Richardson numbers (Ri) are also studied as an independent way of looking at the internal mixing. Both the x-T distributions of Ri statistics and of mean Ri calculated as the ratio of the mean square bouyancy frequency to the mean square current shear show similar structure. Both the results for Ri and K (the coefficient of diapycnal turbulent diffusion of heat) from the NCCM calculation indicate strongest internal mixing and upwelling at the base of an inclined frontal zone.General K(Ri) relationships are discussed and a particular form is chosen and calibrated with the mean Ri and mean K results from a number of common bins in x-T space. The best choice K(Ri) is then used to calculate new, improved distributions of the diapycnal exchanges. Maximum values for K and upwelling at the base of the frontal layer are ∼5 cm2 s−1 and ∼7 × 10−3 cm−1. A procedure is described for calculating mean upwelling circulation from known distributions of diapycnal exchanges. As expected, the circulation based on the diapycnal exchanges from the K(Ri) model agrees best with observed current structure, calculated Ekman transport in the surface layer and heat balance requirements. The heat balance calculation indicated that shoreward eddy heat flux supplies more heat to the nearshore surface layers of northern Peru than direct surface heating. It is concluded that the K(Ri) results obtained here may have a certain universal character and one of the best ways to accurately estimate coastal upwelling circulation may be to observe the Richardson number

Benthic Microfloral Production on the West and Gulf Coasts of the United States: Techniques for Analyzing Dynamic Data (Entropy Data Analysis).

The objective of this study was to compare benthic microfloral production on the west and gulf coasts of the U.S.A., and to determine what factors govern that production. Intensive, month long field studies were conducted at two sites in a salt marsh lagoon (Mugu Lagoon) in southern California and at two sites in a shallow water estuary (Barataria Estuary) in southwest Louisiana. For both studies, fluctuations in production during a single month approximated those measured previously over an entire year: daily production varied from 0 to 1500 mg C (.) m(\u27-2). A comparison was made between the sources of error likely to be introduced by insufficient sampling in space and time with the error likely to be introduced by the commonly used conversions of hourly productivity to monthly production. The error introduced by inadequate sampling in space and time outweighs the error introduced by converting measured midday productivity to estimated monthly production. For a given number of days per month, sampling at a few stations several times per month is more informative than sampling at many stations once or twice a month. The cumulative error introduced in the annual estimates by insufficient sampling and inappropriate conversion assumptions accounts for the total range of variation in existing annual estimates for different regions of the world. The data sets were not amenable to standard statistical analyses, because correlations between productivity and the individual environmental variables varied through time. Multichannel information analysis indicated that the collective information for all the measured variables produced periodicities of 14 days, 7 days, or less, reflecting the dynamic nature of the benthic microfloral system and the need for frequent sampling. Entropy data analysis indicated that no single variable limits productivity. Instead, the variables integrate into factors and these factors change over time. At all 4 sites, productivity was influenced primarily by several different types of disturbance: tidal currents, meteorological and man-made waves, and direct and indirect disturbance by macrofauna were most important. Solar radiation became important in the absence of disturbance. The concept of an ecosystem grammar is developed as a tool for describing the rules that govern the interrelationships amongst variables

A theory of time-dependent upwelling induced by a spacially- and temporally-varying wind with emphasis on the effects of a seabreeze-landbreeze cycle

Solutions are derived for the velocity field of a model ocean - homogeneous, infinitely deep and wide, and bounded on one side by a vertical wall - resulting from a wind which suddenly starts to blow. This model wind consists of a trade wind and a land-seabreeze, both of which decrease exponentially from shore. These solutions are then analysed for various limiting cases. Due to the linearity ot the model, these solutions are separable and yield for t→ ∞ 1.) steady-state upwelling of about 6 X 10-3 cm/sec within the coastal Ekman layer of width O (50 km) as well as sinking across the width of the trade wind belt and 2.) horizontal and vertical oscilliations of daily period. At 20° the vertical oscillations have amplitudes O (10-2 cm/sec) within the coastal Ekman layer and O (10-3 cm/sec) outside of it. In addition the amplitudes of these oscillations are found to be functions of latitude, exhibiting a resonance point at 30° where the inertial frequency and the land-sea-breeze frequency are the same. lt is postulated that the "unbounded" wave energy around 30° is transfered to the turbulent field resulting in increased mixing by 30°. This could possibly explain the relative temperature minima observed there

Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration

The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks.Comment: v1: 16 pages, 4 figures, 7 supplementary files; v2: 15 pages, 4 figures, 7 supplementary files, corrected typos, revised title, updated according to revisions made through publication proces

Allocation of time in reading

How teachers allocated instructional time in reading classes served as the focus of this study. Twenty teachers were observed during reading sessions to answer two research questions. For question 1, how do teachers allocate time, observations indicated that teachers used class time in the following increments: reading and responding 35.47%; listening and discussing 24.89%; waiting 8.36%; completing skill development activities 20.28%; telling, writing, and narrating 7.52%; and devoting 3.47% of the remaining instructional time to other activities. Question 2, does time allocated for reading coordinated text exceed more than 50% of the total time designated for reading instruction, answer appeared to be no. Teachers observed in this study allocated only 35% of instructional time for children to read and respond to concentrated amounts of coordinated text. Recommended time allocations that stated that time reading should exceed the time allocated to all other reading class activities was not observed

Implementation of methane cycling for deep time, global warming simulations with the DCESS Earth System Model (Version 1.2)

Geological records reveal a number of ancient, large and rapid negative excursions of the carbon-13 isotope. Such excursions can only be explained by massive injections of depleted carbon to the Earth system over a short duration. These injections may have forced strong global warming events, sometimes accompanied by mass extinctions such as the Triassic-Jurassic and end-Permian extinctions 201 and 252 million years ago, respectively. In many cases, evidence points to methane as the dominant form of injected carbon, whether as thermogenic methane formed by magma intrusions through overlying carbon-rich sediment or from warming-induced dissociation of methane hydrate, a solid compound of methane and water found in ocean sediments. As a consequence of the ubiquity and importance of methane in major Earth events, Earth system models for addressing such events should include a comprehensive treatment of methane cycling but such a treatment has often been lacking. Here we implement methane cycling in the Danish Center for Earth System Science (DCESS) model, a simplified but well-tested Earth system model of intermediate complexity. We use a generic methane input function that allows variation in input type, size, timescale and ocean-atmosphere partition. To be able to treat such massive inputs more correctly, we extend the model to deal with ocean suboxic/anoxic conditions and with radiative forcing and methane lifetimes appropriate for high atmospheric methane concentrations. With this new model version, we carried out an extensive set of simulations for methane inputs of various sizes, timescales and ocean-atmosphere partitions to probe model behavior. We find that larger methane inputs over shorter timescales with more methane dissolving in the ocean lead to ever-increasing ocean anoxia with consequences for ocean life and global carbon cycling. Greater methane input directly to the atmosphere leads to more warming and, for example, greater carbon dioxide release from land soils. Analysis of synthetic sediment cores from the simulations provides guidelines for the interpretation of real sediment cores spanning the warming events. With this improved DCESS model version and paleo-reconstructions, we are now better armed to gauge the amounts, types, timescales and locations of methane injections driving specific, observed deep-time, global warming events.FONDECYT (Chile) 1150913 Chilean ICM grant NC12006