Robert N. Swift

Bio: Robert N. Swift is an academic researcher from Wallops Flight Facility. The author has contributed to research in topics: Wind wave & Lidar. The author has an hindex of 27, co-authored 50 publications receiving 4586 citations.

Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean

Abstract: The idea that iron might limit phytoplankton growth in large regions of the ocean has been tested by enriching an area of 64 km2 in the open equatorial Pacific Ocean with iron This resulted in a doubling of plant biomass, a threefold increase in chlorophyll and a fourfold increase in plant production Similar increases were found in a chlorophyll-rich plume down-stream of the Galapagos Islands, which was naturally enriched in iron These findings indicate that iron limitation can control rates of phytoplankton productivity and biomass in the ocean

Greenland Ice Sheet: High-Elevation Balance and Peripheral Thinning

Abstract: Aircraft laser-altimeter surveys over northern Greenland in 1994 and 1999 have been coupled with previously reported data from southern Greenland to analyze the recent mass-balance of the Greenland Ice Sheet. Above 2000 meters elevation, the ice sheet is in balance on average but has some regions of local thickening or thinning. Thinning predominates at lower elevations, with rates exceeding 1 meter per year close to the coast. Interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet, sufficient to raise sea level by 0.13 millimeter per year-approximately 7% of the observed rise.

Greenland ice sheet: increased coastal thinning

Abstract: Repeated laser-altimeter surveys and modelled snowfall/summer melt show average ice loss from Greenland between 1997 and 2003 was 80 ± 12 km3 yr-1, compared to about 60 km3 yr -1 for 1993/4-1998/9. Half of the increase was from higher summer melting, with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation. Velocities of one large glacier almost doubled between 1997 and 2003, resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003. Copyright 2004 by the American Geophysical Union.

Evaluation of Airborne Topographic Lidar* for Quantifying Beach Changes

Abstract: A scanning airborne topographic lidar was evaluated for its ability to quantify beach topography and changes during the Sandy Duck experiment in 1997 along the North Carolina coast. Elevation estimates, acquired with NASA's Airborne Topographic Mapper (ATM), were compared to elevations measured with three types of ground-based measurements-1) differential GPS equipped all-terrain vehicle (ATV) that surveyed a 3-km reach of beach from the shoreline to the dune, 2) GPS antenna mounted on a stadia rod used to intensely survey a different 100 m reach of beach, and 3) a second GPS-equipped ATV that surveyed a 70-km-long transect along the coast. Over 40,000 individual intercomparisons between ATM and ground surveys were calculated. RMS vertical differences associated with the ATM when compared to ground measurements ranged from 13 to 19 cm. Considering all of the intercomparisons together, RMS = 15 cm. This RMS error represents a total error for individual elevation estimates including uncertainties associated with random and mean errors. The latter was the largest source of error and was attributed to drift in differential GPS. The - 15 cm vertical accuracy of the ATM is adequate to resolve beach-change signals typical of the impact of storms. For example, ATM surveys of Assateague Island (spanning the border of MD and VA) prior to and immediately following a severe northeaster showed vertical beach changes in places greater than 2 m, much greater than expected errors associated with the ATM. A major asset of airborne lidar is the high spatial data density. Measurements of elevation are acquired every few m2 over regional scales of hundreds of kilometers. Hence, many scales of beach morphology and change can be resolved, from beach cusps tens of meters in wavelength to entire coastal cells comprising tens to hundreds of kilometers of coast. Topographic lidars similar to the ATM are becoming increasingly available from commercial vendors and should, in the future, be widely used in beach surveying.

Accuracy of airborne laser altimetry over the Greenland ice sheet

Abstract: During September 1991, April 1992 and June/July 1993, a NASA P–3 aircraft, equipped with a scanning laser altimeter, flew numerous transects of the Greenland ice sheet. The aeroplane location was measured precisely using dilTerential Global Positioning System (GPS) surveying techniques, allowing all altimetry data to be converted into measurements of ice-surface elevation relative to the Earth ellipsoid. Results from flight data indicate that icc-surface elevations can be reliably measured to an accuracy of ∼20cm (and possibly to ∼s lOcm) over baselines of more than seven hundred kilometres.

Tipping elements in the Earth's climate system

Abstract: The term "tipping point" commonly refers to a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system. Here we introduce the term "tipping element" to describe large-scale components of the Earth system that may pass a tipping point. We critically evaluate potential policy-relevant tipping elements in the climate system under anthropogenic forcing, drawing on the pertinent literature and a recent international workshop to compile a short list, and we assess where their tipping points lie. An expert elicitation is used to help rank their sensitivity to global warming and the uncertainty about the underlying physical mechanisms. Then we explain how, in principle, early warning systems could be established to detect the proximity of some tipping points.

The Ecology of Phytoplankton

Abstract: Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

Lidar Remote Sensing for Ecosystem Studies

Abstract: Articles R emote sensing has facilitated extraordinary advances in the modeling, mapping, and understanding of ecosystems. Typical applications of remote sensing involve either images from passive optical systems, such as aerial photography and Landsat Thematic Mapper (Goward and Williams 1997), or to a lesser degree, active radar sensors such as RADARSAT (Waring et al. 1995). These types of sensors have proven to be satisfactory for many ecological applications , such as mapping land cover into broad classes and, in some biomes, estimating aboveground biomass and leaf area index (LAI). Moreover, they enable researchers to analyze the spatial pattern of these images. However, conventional sensors have significant limitations for ecological applications. The sensitivity and accuracy of these devices have repeatedly been shown to fall with increasing aboveground biomass and leaf area index (Waring et al. 1995, Carlson and Ripley 1997, Turner et al. 1999). They are also limited in their ability to represent spatial patterns: They produce only two-dimensional (x and y) images, which cannot fully represent the three-dimensional structure of, for instance, an old-growth forest canopy.Yet ecologists have long understood that the presence of specific organisms, and the overall richness of wildlife communities, can be highly dependent on the three-dimensional spatial pattern of vegetation (MacArthur and MacArthur 1961), especially in systems where biomass accumulation is significant (Hansen and Rotella 2000). Individual bird species, in particular, are often associated with specific three-dimensional features in forests (Carey et al. 1991). In addition, other functional aspects of forests, such as productivity, may be related to forest canopy structure. Laser altimetry, or lidar (light detection and ranging), is an alternative remote sensing technology that promises to both increase the accuracy of biophysical measurements and extend spatial analysis into the third (z) dimension. Lidar sensors directly measure the three-dimensional distribution of plant canopies as well as subcanopy topography, thus providing high-resolution topographic maps and highly accurate estimates of vegetation height, cover, and canopy structure. In addition , lidar has been shown to accurately estimate LAI and aboveground biomass even in those high-biomass ecosystems where passive optical and active radar sensors typically fail to do so. The basic measurement made by a lidar device is the distance between the sensor and a target surface, obtained by determining the elapsed time between the emission of a short-duration laser pulse and the arrival of the reflection of that pulse (the return signal) at the sensor's receiver. Multiplying this …

A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization

Abstract: Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis' For this reason, it is important to understand the response of pelagic biota to increased iron supply Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days This drawdown was mostly due to the proliferation of diatom stocks But downward export of biogenic carbon was not increased Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction