Lisa Greer

The 13C Suess effect in scleractinian corals mirror changes in the anthropogenic CO2 inventory of the surface oceans

[1] New δ 13 C data are presented from 10 coral skeletons collected from Florida and elsewhere in the Caribbean (Dominica, Dominican Republic, Puerto Rico, and Belize). These corals range from 96 to 200 years in age and were collected between 1976 and 2002. The change in the δ 13 C of the skeletons from these corals between 1900 and 1990 has been compared with 27 other published coral records from the Atlantic, Pacific, and Indian Oceans. The new data presented here make possible, for the first time, a global comparison of rates of change in the δ 13 C value of coral skeletons. Of these records, 64% show a statistically significant (p < 0.05) decrease in δ 13 C towards the modem day (23 out of 37). This decrease is attributable to the addition of anthropogenically derived CO 2 ( 13 C Suess effect) to the atmosphere. Between 1900 and 1990, the average rate of change of the δ 13 C in all the coral skeletons living under open oceanic conditions is approximately - 0.01%o yr ―1 . In the Atlantic Ocean the magnitude of the decrease since 1960,―0.019 yr ―1 ±0.015‰, is essentially the same as the decrease in the δ 13 C of atmospheric CO 2 and the δ 13 C of the oceanic dissolved inorganic carbon (-0.023 to -0.029‰ yr ―1 ), while in the Pacific and Indian Oceans the rate is more variable and significantly reduced (-0.007‰ yr ―1 ±0.013). These data strongly support the notion that (i) the δ 13 C of the atmosphere controls ambient δ 13 C of the dissolved inorganic carbon which in turn is reflected in the coral skeletons, (ii) the rate of decline in the coral skeletons is higher in oceans with a greater anthropogenic CO 2 inventory in the surface oceans, (iii) the rate of δ 13 C decline is accelerating. Superimposed on these secular variations are controls on the δ 13 C in the skeleton governed by growth rate, insolation, and local water masses.

Real-Time Analysis of Student Comprehension: An Assessment of Electronic Student Response Technology in an Introductory Earth Science Course

Electronic student response technologies (SRT) are capable of assessing teaching and learning methods in real time, and they offer an exceptional means of introducing active learning protocols in classes with large enrollments. These wireless systems allow students to key in responses with remote control units to questions posed by an instructor in the classroom. Student responses then are displayed in real time, allowing both students and instructors to gauge student comprehension instantaneously. From Spring 2002 to Spring 2003, we utilized SRT in 4 sections of a high-enrollment introductory Earth Science course (Geosc 020: Planet Earth) at Penn State University. We conducted a multi-faceted assessment of the use of SRT in our course that included quantitative and qualitative perception data from students enrolled in the course and faculty/administrator visitors to our classroom. Our preliminary assessment of the pedagogical merits of SRT in our course suggests that this technology is an effective tool for introductory geoscience education.

Using Conceptests to Assess and Improve Student Conceptual Understanding in Introductory Geoscience Courses

Conceptests are higher-order multiple-choice questions that focus on one key concept of an instructors major learning goals for a lesson. When coupled with student interaction through peer instruction, conceptests represent a rapid method of formative assessment of student understanding, require minimal changes to the instructional environment and introduce many of the recognized principles of effective teaching that enhance student learning. In this study, instructors from several different institutions developed over 300 conceptests for the geosciences. These instructors then used this suite of concept questions in a wide range of classroom settings, including large introductory general education Earth Science courses for non-majors at open enrollment institutions, smaller physical geology classes suitable for majors at private colleges, and in introductory geology laboratory settings. Results of pre- and post-class Geoscience Concept Inventory (GCI) testing and qualitative feedback from students and instructors showed that conceptests increased attendance, improved student satisfaction, and enhanced student achievement. Participating instructors found implementation of conceptests into their classes straightforward and required less than 30 minutes of preparation per class. The conceptest question database is available on-line for geoscience instructors.

The Use of Proxy Chemical Records in Coral Skeletons to Ascertain Past Environmental Conditions in Florida Bay

This paper will discuss the use of chemical proxies in coral skeletons to reconstruct the history of salinity (from the δ18O of the skeleton) and nutrients in the water (from the δ13C) in Florida Bay between 1824 and 1994. Monthly salinity and water temperature data collected since 1989 were used to establish a correlation between salinity, temperature, and the δ18O of the skeleton of the coralSolenastrea bournoni from Lignumvitae Basin in Florida Bay. This relationship explains over 50% of the variance in the δ18O of the skeleton. Assuming that interannual variations in the temperature of the water are small, we have applied this relationship to the δ18O measured in the coral skeleton collected from Lignumvitae Basin which has a record between 1824 and 1993. These data provide a revised estimate of salinity variation in Lignumvitae Basin for the period when historical records for salinity were not available, and show that the highest salinity events occurred in the past 30 yr. Using the relationships between the salinity in Lignumvitate Basin and other basins, obtained using a modern dataset, we are able to estimate ranges in salinity for other portions of Florida Bay. Skeletons of specimens of the coral speciesSiderastrea radians collected from other areas of Florida Bay show similar patterns in the δ18O over the past 10 yr, indicating that corals in most portions of Florida Bay are recording salinity variations in their skeletons and therefore support the idea that salinity variations in different portions of Florida Bay can be related. Fluorescence analysis of the coral from Lignumvitae Basin shows a large change in the magnitude of the 10-yr signal coincident with the construction of the railway, confirming that this event had a significant impact upon Florida Bay. The δ13C of the coral skeletons reveals a long-term history of the oxidation of organic material, fixation of carbon by photosynthesis (algal blooms), and the intrusion of marine water into the bay. Since the construction of the railway from Miami to Key West there has been a long-term decrease in the δ13C of the coral skeleton from Lignumvitae Basin, suggesting the increased oxidation of organic material in this area. This decrease in δ13C appears to have reached a minimum value around 1984 and has increased since this time in the western portions of Florida Bay. The increase may be related to the algal blooms prevalent in the area or alternatively could result from intrusion of more marine water. In the eastern areas, a small increase in the δ18C between 1984 and 1988 was followed by further decline suggesting more oxidation of organic material. We have also attempted to use the concentration of barium in the coral skeleton as a proxy indicator of the nutrient status in Florida Bay.

How vulnerable is Acropora cervicornis to environmental change? Lessons from the early to middle Holocene

The coral Acropora cervicornis is considered a modern environmental indicator species, vulnerable to anthropogenic stress and rapidly disappearing throughout the Caribbean. Causes for its decline have been attributed to both natural and anthropogenic factors. Physical and geochemical data are used to explore conditions under which this species thrived in early to middle Holocene reef deposits (ca. 9.4–5.4 ka) of the Enriquillo Valley, southwestern Dominican Republic. This study shows that A. cervicornis fl ourished during a 4000 yr period spanning the Holocene Thermal Maximum, and high-resolution radiocarbon dating reveals continuous growth for at least 2000 yr. Holocene A. cervicornis survived large-scale climate and environmental changes that included high temperatures, variable salinity, hurricanes, and rapid sea-level rise with remarkable resilience. Our data suggest that the recent decline in A. cervicornis is anomalous and likely tied to ecosystem change beyond natural causes.

Field-based Instruction as Part of a Balanced Geoscience Curriculum at Washington and Lee University

Traditionally at Washington and Lee University teaching in the field has been the core of our geology curriculum. We emphasize fieldwork at all levels of our instruction from the field-based introductory courses to our senior theses. We are fortunate to be located in a geologically diverse location (in the Valley and Ridge of Virginia and within minutes of the Blue Ridge Mountains). The close proximity of geologic variety allows us to spend nearly every class or laboratory period outside. We view fieldwork, however, as just the beginning of geoscience education. A crucial aspect of field geology is making observations and synthesizing the data collected. It is equally important for students to have well-developed skills in field methods, in analytical techniques, in computation and modeling, and in synthesis and presentation. To emphasize all of these aspects, our coursework is largely focused on emulating the process of research. Because we have had such a strong field emphasis, we are striving to strike a balance in our curriculum. We will present 3 examples of integrated exercises in our geology courses (including introductory geology, sedimentary geology, and geochemistry).

UNUSUAL HOLOCENE SERPULID-TUFA BIOHERMS, ENRIQUILLO VALLEY, DOMINICAN REPUBLIC: MORPHOLOGIES AND PALEOENVIRONMENTAL IMPLICATIONS

ABSTRACT During the early Holocene, rising waters of the Caribbean Sea flooded the Enriquillo Valley of southwestern Dominican Republic. A fringing coral reef developed and flourished along the margins of the Enriquillo Seaway for several millennia, until the seaway became restricted due to a combination of slowed sea-level rise, tectonic uplift, and increased sedimentation. Following changes in salinity and death of the coral reef by about 5 ka, meter-scale bioherms composed of the tubes of opportunistic, aggregating serpulid worms and associated with carbonate tufa that precipitated from the ancient lake or declining seaway waters formed along the steep walls of the valley over a period of 1,000 years or more. Paleoenvironmental conditions likely conducive to formation of these unusual bioherms include: non-normal marine salinity, warm and restricted waters, periods of stable water level, high Ca2+ and CO32− influx, and moderate wave action. Although apparently rare elsewhere in the rock record, occurrences of serpulid-tufa bioherms provide useful constraints on paleoenvironmental settings. In previous literature, variations in terminology used to describe both tufa and serpulid-tufa bioherms have hindered intersite comparisons. Herein, serpulid-tufa bioherm structures are described at macro-, meso-, and microscales, and the varied bioherm macromorphologies are classified as individual, clustered, terraced, and patch types. These form descriptions are compared with previously published classifications of similar structures; the goal is to facilitate development of a comprehensive and universal classification of serpulid-tufa bioherms to further understand their formation and paleoenvironmental significance.