Search Results

This chapter describes the role that paleolimnological studies have played in reconstructing the geomorphological origin and development of high latitude lakes. A description is provided on how both organic and inorganic components incorporated into lake sediments record changes within lakes as well as in the surrounding environment. This allows tracking of past changes in climate, hydrology, vegetation, sea level, human impacts on fish and wildlife populations, ultraviolet radiation, and atmospheric and terrestrial pollutants. The chapter covers some synthesis studies that have combined paleolimnological data from multiple lakes across the Arctic and Antarctic in order to identify the magnitude and direction of environmental changes at regional to continental scales. The geographic scope of the chapter includes the Arctic north of the tree line (tundra or polar desert catchments), the Antarctic continent and Antarctic Peninsula region, with occasional reference to the warmer sub-Arctic and sub-Antarctic regions.

This chapter studies the importance, the evidence, and the causes of sea level changes. Sea levels are low during glacials and are high during interglacials. The rapid rise in the sea level in post-glacial times caused the submerging of many coastlines and the rise of the areas covered in ice caps in the Pleistocene because of their loss of ice burden.

The Pacific Basin comprises two distinct parts, the continental Pacific Rim and the oceanic Pacific Ocean and Islands. Rather than being a single giant basin, the modern Pacific Basin is actually a series of basins divided by ranges of mountains (mostly underwater). Despite their diversity, these ocean basins share a common oceanic origin, broadly unrelated to the origins of the continents, which are mostly much older. This chapter outlines the background to the dynamic condition of the Pacific Basin. It explains its evolution and describes the processes by which movements of the land (tectonic movements) have taken place. Topics covered include the history of the Pacific; uplift, subsidence, sea-level changes in the Pacific; and the inability to verify theories (or models) that seek to explain historical processes of earth-surface evolution because they deal with things that happened in the past.

This chapter reviews the physical factors that shape tidal-marsh landscapes in the San Francisco estuary and discusses functional classes of landscape elements. Physical processes covered include natural variability in salinity, responses to human-mediated surface-water management practices, tides, and rates of sea-level rise. Landscape elements include the marsh plain, fringing low marsh, marsh-upland ecotone, tidal channels, berms, and salt ponds, pannes, and salinas. Studies of tidal-channel structure, function, and stability are reviewed, with an emphasis on variations in planform and sinuosity, slumps, tidal asymmetry, and hydraulic geometry relations. Keys areas for future research are identified, with a focus on identifying how tidal wetlands are responding and will respond to present and future increased inundation regimes.

On the work floor, research on past climates is known as paleoclimatology, and research on past oceans as paleoceanography. But they are very tightly related, and we shall discuss both combined under the one term of paleoclimatology. Within paleoclimatology, interests are spread over three fundamental fields. The first field is concerned with dating ancient evidence and is referred to as chronological studies. These studies are essential because all records of past climate change need to be dated as accurately as possible to ensure that we know when the studied climate changes occurred, how fast they were, and whether changes seen in various components of the climate system happened at the same time or at different times. The second field concerns observational studies, where the observations can be of different types. Some are direct measurements; for example, sunspot counts or temperature records. Some are historical, written accounts of anecdotal evidence, such as reports on the frequency of frozen rivers, floods, or droughts. Such records are very local and often subjective, so they are usually no good as primary evidence. But they can offer great support and validation to reconstructions from other tools. Besides direct and anecdotal data, we encounter the dominant type of evidence used in the discipline. These are the so- called proxy data, or proxies. Proxies are indirect measures that approximate (hence the name proxy) changes in important climate- system variables, such as temperature, CO2 concentrations, nutrient concentrations, and so on. This chapter outlines some of the most important proxies. The third field in paleoclimatology concerns modeling. It employs numerical models for climate system simulation and simpler classes of so-called box- models. Numerical climate models range from Earth System models that are relatively crude and can therefore be set to run simulations of many thousands of years, to very complex and refined coupled models that are computationally very greedy and thus give simulations of great detail but only over short intervals of time. Box- models are much simpler and faster to run, and they are most used in modeling of the carbon cycle or other geochemical properties.

The reptiles of the islands of the Sea of Cortés have provided many opportunities to test ecological and biogeographical hypotheses because they support a diverse fauna with much insular endemism; are numerous and of varying ages and degrees of isolation; are relatively undisturbed by human activity and introduced species; and have a relatively well-understood geological history (see chap. 2). In particular, contrasts of mainland and island reptile populations in the region have resulted in significant progress in testing theories of island biogeography, principles of ecological character displacement, ecological release, density compensation, and vicariance biogeography (see chap. 8). The reptiles, being conspicuous in these arid habitats, have attracted relatively more research attention than other vertebrates, and today we have a reasonably complete picture of at least which species are on which islands. Since the first edition of this book, nearly 20 years ago, there have been only 15 new records for the major islands, of which all but one are of snakes. In this chapter I review the basic elements of reptilian island biogeography in the Sea of Cortés with an emphasis on ecological factors shaping distributions and evolutionary trajectories. I first examine the patterns of species diversity and association across islands. I then take a closer look at some particular island forms, reviewing features of their life history that seem divergent from mainland relatives. In this regard I present some new data from a long-term study of two insular species of chuckwallas. Finally, I review patterns of population density across islands and their possible determinants. A recurrent debate in island biogeography centers on the relative importance of contemporary and ongoing ecological factors relative to historical circumstances in accounting for the number and the identities of species on islands. Historical biogeographers typically view the number of species on an island as being determined by the availability of appropriate habitats. They see changes in species composition chiefly as a consequence of alteration of the mix of habitats due to climatic change (e.g., Pregill and Olson 1980; Olson and Hilgartner 1982); extinctions are posited to occur in waves, as old habitats disappear and new ones become available.

In The Log of the Sea of Cortez, that memorable treatise of science, adventure, and philosophy, John Steinbeck (1951) made bare mention of mammals. Of course, the main purpose of that effort was to chronicle a trip to the Gulf of California to collect invertebrates in the company of Steinbeck’s friend and scientist, Ed Ricketts. The party visited four islands—Tiburón, Coronados, San José, and Espíritu Santo. At anchor off Isla Tiburόn, Steinbeck reported a swarm of bats that approached their boat. One bat was collected but, to the best of our knowledge, it was never identified or preserved. Aside from some descriptions of taxa (e.g., Butt 1932), relatively little was known at the time about mammals from islands in the Sea of Cortés. There is now a reasonably rich history of systematic and biogeographic studies of mammals in and adjacent to the Sea of Cortés (for general reviews, see Orr 1960; Huey 1964; Lawlor 1983; and Hafner and Riddle 1997). Here we summarize much of that information and explore biogeographic patterns that emerge from it, add important recent records of bats, and evaluate new evidence about the origins of insular faunas and the ecological processes and human impacts that affect colonization and persistence of mammals on gulf islands. The terrestrial mammalian fauna of islands in the Sea of Cortés (including islands off the Pacific coast of Baja California) comprises 45 species, of which 18 currently are recognized as endemics (but see below), representing 5 orders, 9 families, and 14 genera (app. 12.1). Collectively they share relationships with mainland representatives on both sides of the gulf and are divisible into 28 clades of species or species groups (app. 12.2). Rodents are disproportionately represented, constituting a total of 35 species and 76 of 97 total insular occurrences, and they are the only nonvolant mammals to become established on distant oceanic islands. In addition, except for the few species of lagomorphs, which occur only on landbridge islands, a greater proportion of mainland species of rodents occurs on islands than is the case for other groups of mammals.

According to Imamura (1937: 123), the term tunami or tsunami is a combination of the Japanese word tu (meaning a port) and nami (a long wave), hence long wave in a harbour. He goes on to say that the meaning might also be defined as a seismic sea-wave since most tsunamis are produced by a sudden dip-slip motion along faults during major earthquakes. Other submarine or coastal phenomena, however, such as volcanic eruptions, landslides, and gas escapes, are also known to cause tsunamis. According to Van Dorn (1968), ‘tsunami’ is the Japanese name for the gravity wave system formed in the sea following any large-scale, short-duration disturbance of the free surface. Tsunamis fall under the general classification of long waves. The length of the waves is of the order of several tens or hundreds of kilometres and tsunamis usually consist of a series of waves that approach the coast with periods ranging from 5 to 90 minutes (Murty 1977). Some commonly used terms that describe tsunami wave propagation and inundation are illustrated in Figure 17.2. Because of the active lithospheric plate convergence, the Mediterranean area is geodynamically characterized by significant volcanism and high seismicity as discussed in Chapters 15 and 16 respectively. Furthermore, coastal and submarine landslides are quite frequent and this is partly in response to the steep terrain of much of the basin (Papadopoulos et al. 2007a). Tsunamis are among the most remarkable phenomena associated with earthquakes, volcanic eruptions, and landslides in the Mediterranean basin. Until recently, however, it was widely believed that tsunamis either did not occur in the Mediterranean Sea, or they were so rare that they did not pose a threat to coastal communities. Catastrophic tsunamis are more frequent on Pacific Ocean coasts where both local and transoceanic tsunamis have been documented (Soloviev 1970). In contrast, large tsunami recurrence in the Mediterranean is of the order of several decades and the memory of tsunamis is short-lived. Most people are only aware of the extreme Late Bronge Age tsunami that has been linked to the powerful eruption of Thera volcano in the south Aegean Sea (Marinatos 1939; Chapter 15).