Antarctic Volcanic Flux Ratios from Law Dome Ice Cores

Explosive volcanic eruptions can inject large quantities of sulphur dioxide into the stratosphere. The aerosols that result from oxidation of the sulphur dioxide can produce significant cooling of the troposphere by reflecting or absorbing solar radiation. It is possible to obtain an estimate of the relative stratospheric sulphur aerosol concentration produced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polar ice cores. Here, we use a non-sea-salt sulphate time series derived from three well-dated Law Dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period AD 1301-1995. We use additional data from other cores to investigate systematic spatial variability in the ratios. Only for the Kuwae eruption (Law Dome ice date AD 1459.5) was the H2SO4 flux larger than that deposited by Tambora (Law Dome ice date AD 1816.7).

The Aeolian Flux of Calcium, Chloride and Nitrate to the McMurdo Dry Valleys Landscape: Evidence from Snow Pit Analysis

We have determined the flux of calcium, chloride and nitrate to the McMurdo Dry Valleys region by analysing snow pits for their chemical composition and their snow accumulation using multiple records spanning up to 48 years. The fluxes demonstrate patterns related to elevation and proximity to the ocean. In general, there is a strong relationship between the nitrate flux and snow accumulation, indicating that precipitation rates may have a great influence over the nitrogen concentrations in the soils of the valleys. Aeolian dust transport plays an important role in the deposition of some elements (e.g. C(2+)) into the McMurdo Dry Valleys' soils. Because of the antiquity of some of the soil surfaces in the McMurdo Dry Valleys regions, the accumulated atmospheric flux of salts to the soils has important ecological consequences. Although precipitation may be an important mechanism of salt deposition to the McMurdo Dry Valley surfaces, it is poorly understood because of difficulties in measurement and high losses from sublimation.

A High-Resolution Record of Atmospheric Dust Composition and Variability Since Ad 1650 from a Mount Everest Ice Core

A Mount Everest ice core analyzed at high resolution for major and trace elements (Sr, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, U, Tl, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co) and spanning the period A. D. 1650- 2002 is used to investigate the sources of and variations in atmospheric dust through time. The chemical composition of dust varies seasonally, and peak dust concentrations occur during the winter-spring months. Significant correlations between the Everest dust record and dust observations at stations suggest that the Everest record is representative of regional variations in atmospheric dust loading. Back-trajectory analysis in addition to a significant correlation of Everest dust concentrations and the Total Ozone Mapping Spectrometer (TOMS) aerosol index indicates that the dominant winter sources of dust are the Arabian Peninsula, Thar Desert, and northern Sahara. Factors that contribute to dust generation at the surface include soil moisture and temperature, and the long-range transport of dust aerosols appears to be sensitive to the strength of 500-mb zonal winds. There are periods of high dust concentration throughout the 350-yr Mount Everest dust record; however, there is an increase in these periods since the early 1800s. The record was examined for recent increases in dust emissions associated with anthropogenic activities, but no recent dust variations can be conclusively attributed to anthropogenic inputs of dust.

Seasonal Geophysical Monitoring of Biogenic Gases in a Northern Peatland: Implications for Temporal and Spatial Variability in Free Phase Gas Production Rates

A set of high resolution surface ground penetrating radar (GPR) surveys, combined with elevation rod ( to monitor surface deformation) and gas flux measurements, were used to investigate in situ biogenic gas dynamics within a northern peatland (Caribou Bog, Maine). Gas production rates were directly estimated from the time series of GPR measurements. Spatial variability in gas production was also investigated by comparing two sites with different geological and ecological attributes, showing differences and/or similarities depending on season. One site characterized by thick highly humified peat deposits (5-6 m), wooded heath vegetation and open pools showed large ebullition events during the summer season, with estimated emissions (based on an assumed range of CH(4) concentration) between 100 and 172 g CH(4) m(-2) during a single event. The other site characterized by thinner less humified peat deposits (2-3 m) and shrub vegetation showed much smaller ebullition events during the same season (between 13 and 23 g CH(4) m(-2)). A consistent period of free-phase gas (FPG) accumulation during the fall and winter, enhanced by the frozen surficial peat acting as a confining layer, was followed by a decrease in FPG after the snow/ice melt that released estimated fluxes between 100 and 200 g CH(4) m(-2) from both sites. Estimated FPG production rates during periods of biogenic gas accumulation ranged between 0.22 and 2.00 g CH(4) m(3) d(-1) and reflected strong seasonal and spatial variability associated with differences in temperature, peat soil properties, and/or depositional attributes (e. g., stratigraphy). Periods of decreased atmospheric pressure coincided with short-period increases in biogenic gas flux, including a very rapid decrease in FPG content associated with an ebullition event that released an estimated 39 and 67 g CH(4) m(-2) in less than 3.5 hours. These results provide insights into the spatial and seasonal variability in production and emission of biogenic gases from northern peatlands.

Sea Level Pressure Variability Over the Southern Indian Ocean Inferred from a Glaciochemical Record in Princess Elizabeth Land, East Antarctica

A 250-year, high-resolution, multivariate ice core record from LGB65 (70degrees50'07"S, 77degrees04'29"E; 1850 m asl), Princess Elizabeth Land (PEL), is used to investigate sea level pressure (SLP) variability over the southern Indian Ocean (SIO). Empirical orthogonal function (EOF) analysis reveals that the first EOF (EOF1) of the glaciochemical record from LGB65 represents most of the variability in sea salt throughout the 250-year record. EOF1 is negatively correlated (95% confidence level and higher) to instrumental mean sea level pressure (MSLP) at Kerguelen and New Amsterdam islands, SIO. On the basis of comparison with NCEP/NCAR reanalysis, strong correlations were found between sea-salt variations and a quasi-stationary low that lies to the north of Prydz Bay, SIO. Comparison with a 250-year-long summer transpolar index (STPI) inferred from sub-Antarctic tree ring records reveals strong coherency. Decadal-scale SLP variability over SIO suggests shifting of the polar vortex. Prominent decadal-scale deepening of the southern Indian Ocean low (SIOL) exists circa 1790, 1810, 1835, 1860, 1880, 1900, and 1940 A. D., continuously after the 1970s, and prominent weakening circa 1750, 1795, 1825, 1850, 1870, 1890, 1910, and 1955 A. D. The LGB65 sea-salt record is characterized by significant decadal-scale variability with a strong similar to21-year periodic structure (99.9% confidence level). The relationship between LGB65 sea salt and solar irradiance changes shows that this periodicity is possibly the solar Hale cycle ( 22 years).

The Polar Expression of ENSO and Sea-Ice Variability as Recorded in a South Pole Ice Core

An annually dated ice core recovered from South Pole (2850 in a.s.l.) in 1995, that covers the period 1487-1992, was analyzed for the marine biogenic sulfur species methanesulfonate (MS). Empirical orthogonal function analysis is used to calibrate the high-resolution MS series with associated environmental series for the period of overlap (1973-92). Utilizing this calibration we present a similar to500 year long proxy record of the polar expression of the El Nino-Southern Oscillation (ENSO) and southeastern Pacific sea-ice extent variations. These records reveal short-term periods of increased (1800-50, 1900-40) and decreased sea-ice extent (1550-1610., 1660-1710, 1760-1800). In general, increased (decreased) sea-ice extent is associated with a higher (lower) frequency of El Nino events.

Satellite-Derived Variability in Chlorophyll, Wind Stress, Sea Surface Height, and Temperature in the Northern California Current System

Satellite-derived data provide the temporal means and seasonal and nonseasonal variability of four physical and biological parameters off Oregon and Washington ( 41 degrees - 48.5 degrees N). Eight years of data ( 1998 - 2005) are available for surface chlorophyll concentrations, sea surface temperature ( SST), and sea surface height, while six years of data ( 2000 - 2005) are available for surface wind stress. Strong cross-shelf and alongshore variability is apparent in the temporal mean and seasonal climatology of all four variables. Two latitudinal regions are identified and separated at 44 degrees - 46 degrees N, where the coastal ocean experiences a change in the direction of the mean alongshore wind stress, is influenced by topographic features, and has differing exposure to the Columbia River Plume. All these factors may play a part in defining the distinct regimes in the northern and southern regions. Nonseasonal signals account for similar to 60 - 75% of the dynamical variables. An empirical orthogonal function analysis shows stronger intra-annual variability for alongshore wind, coastal SST, and surface chlorophyll, with stronger interannual variability for surface height. Interannual variability can be caused by distant forcing from equatorial and basin-scale changes in circulation, or by more localized changes in regional winds, all of which can be found in the time series. Correlations are mostly as expected for upwelling systems on intra-annual timescales. Correlations of the interannual timescales are complicated by residual quasi-annual signals created by changes in the timing and strength of the seasonal cycles. Examination of the interannual time series, however, provides a convincing picture of the covariability of chlorophyll, surface temperature, and surface height, with some evidence of regional wind forcing.

Phytoplankton Scales of Variability in the California Current System: 1. Interannual and Cross-Shelf Variability

In the California Current System, strong mesoscale variability associated with eddies and meanders of the coastal jet play an important role in the biological productivity of the area. To assess the dominant timescales of variability, a wavelet analysis is applied to almost nine years (October 1997 to July 2006) of 1-km-resolution, 5-day-averaged, Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll a (chl a) concentration data. The dominant periods of chlorophyll variance, and how these change in time, are quantified as a function of distance offshore. The maximum variance in chlorophyll occurs with a period of similar to 100-200 days. A seasonal cycle in the timing of peak variance is revealed, with maxima in spring/summer close to shore (20 km) and in autumn/winter 200 km offshore. Interannual variability in the magnitude of chlorophyll variance shows maxima in 1999, 2001, 2002, and 2005. There is a very strong out-of-phase correspondence between the time series of chlorophyll variance and the Pacific Decadal Oscillation (PDO) index. We hypothesize that positive PDO conditions, which reflect weak winds and poor upwelling conditions, result in reduced mesoscale variability in the coastal region, and a subsequent decrease in chlorophyll variance. Although the chlorophyll variance responds to basin-scale forcing, chlorophyll biomass does not necessarily correspond to the phase of the PDO, suggesting that it is influenced more by local-scale processes. The mesoscale variability in the system may be as important as the chl a biomass in determining the potential productivity of higher trophic levels.

Interannual Variability in Timing of Bloom Initiation in the California Current System

In the California Current System the spring transition from poleward to equatorward alongshore wind stress heralds the beginning of upwelling-favorable conditions. The phytoplankton response to this transition is investigated using 8 years ( 1998-2005) of daily, 4-km resolution, Sea-viewing Wide Field of view Sensor ( SeaWiFS) chlorophyll a concentration data. Cluster analysis of the chlorophyll a time series at each location is used to separate the inshore upwelling region from offshore and oligotrophic areas. An objective method for estimating the timing of bloom initiation is used to construct a map of the mean bloom start date. Interannual variability in bloom timing and magnitude is investigated in four regions: 45 degrees N - 50 degrees N, 40 degrees N - 45 degrees N, 35 degrees N - 40 degrees N and 20 degrees N - 35 degrees N. Daily satellite derived wind data ( QuikSCAT) allow the timing of the first episode of persistently upwelling favorable winds to be estimated. Bloom initiation generally coincides with the onset of upwelling winds ( +/- 15 days). South of similar to 35 degrees N, where winds are southward year-round, the timing of increased chlorophyll concentration corresponds closely to timing of the seasonal increase in upwelling intensity. A 1-D model and satellite derived photosynthetically available radiation data are used to estimate time series of depth- averaged irradiance. In the far north of the region (> 46 degrees N) light is shown to limit phytoplankton growth in early spring. In 2005 the spring bloom in the northern regions (> 35 degrees N) had a "false start''. A sharp increase in chl a in February quickly receded, and a sustained increase in biomass was delayed until July. We hypothesize that this resulted in a mismatch in timing of food availability to higher trophic levels.

Effects of Surface Forcing on Interannual Variability of the Fall Phytoplankton Bloom in the Gulf of Maine Revealed Using a Process-Oriented Model

SeaWiFS (Sea-viewing Wide Field-of-view Sensor) chlorophyll data revealed strong interannual variability in fall phytoplankton dynamics in the Gulf of Maine, with 3 general features in any one year: (1) rapid chlorophyll increases in response to storm events in fall; (2) gradual chlorophyll increases in response to seasonal wind-and cooling-induced mixing that gradually deepens the mixed layer; and (3) the absence of any observable fall bloom. We applied a mixed-layer box model and a 1-dimensional physical-biological numerical model to examine the influence of physical forcing (surface wind, heat flux, and freshening) on the mixed-layer dynamics and its impact on the entrainment of deep-water nutrients and thus on the appearance of fall bloom. The model results suggest that during early fall, the surface mixed-layer depth is controlled by both wind-and cooling-induced mixing. Strong interannual variability in mixed-layer depth has a direct impact on short-and long-term vertical nutrient fluxes and thus the fall bloom. Phytoplankton concentrations over time are sensitive to initial pre-bloom profiles of nutrients. The strength of the initial stratification can affect the modeled phytoplankton concentration, while the timing of intermittent freshening events is related to the significant interannual variability of fall blooms.

North Pacific Carbon Cycle Response to Climate Variability on Seasonal to Decadal Timescales

Climate variability drives significant changes in the physical state of the North Pacific, and there may be important impacts of this variability on the upper ocean carbon balance across the basin. We address this issue by considering the response of seven biogeochemical ocean models to climate variability in the North Pacific. The models' upper ocean pCO(2) and air-sea CO(2) flux respond similarly to climate variability on seasonal to decadal timescales. Modeled seasonal cycles of pCO(2) and its temperature- and non-temperature-driven components at three contrasting oceanographic sites capture the basic features found in observations (Takahashi et al., 2002, 2006; Keeling et al., 2004; Brix et al., 2004). However, particularly in the Western Subarctic Gyre, the models have difficulty representing the temporal structure of the total pCO(2) seasonal cycle because it results from the difference of these two large and opposing components. In all but one model, the air-sea CO(2) flux interannual variability (1 sigma) in the North Pacific is smaller ( ranges across models from 0.03 to 0.11 PgC/yr) than in the Tropical Pacific ( ranges across models from 0.08 to 0.19 PgC/yr), and the time series of the first or second EOF of the air-sea CO(2) flux has a significant correlation with the Pacific Decadal Oscillation (PDO). Though air-sea CO(2) flux anomalies are correlated with the PDO, their magnitudes are small ( up to +/- 0.025 PgC/yr ( 1 sigma)). Flux anomalies are damped because anomalies in the key drivers of pCO(2) ( temperature, dissolved inorganic carbon (DIC), and alkalinity) are all of similar magnitude and have strongly opposing effects that damp total pCO(2) anomalies.

Phytoplankton Scales of Variability in the California Current System: 2. Latitudinal Variability

The California Current System encompasses a southward flowing current which is perturbed by ubiquitous mesoscale variability. The extent to which latitudinal patterns of physical variability are reflected in the distribution of biological parameters is poorly known. To investigate the latitudinal distribution of chlorophyll variance, a wavelet analysis is applied to nearly 9 years (October 1997 to July 2006) of 1-km-resolution Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll concentration data at 5-day resolution. Peaks in the latitudinal distribution of chlorophyll variance coincide with features of the coastal topography. Maxima in variance are located offshore of Vancouver Island and downstream of Heceta Bank, Cape Blanco, Point Arena, and possibly Point Conception. An analysis of dominant wavelengths in the chlorophyll data reveals a transfer of energy into smaller scales is generated in the vicinity of the coastal capes. The latitudinal distribution of variance in sea level anomaly corresponds closely to the chlorophyll variance in the nearshore region (<100 km offshore), suggesting that the same processes determine the distribution of both. Farther offshore, there is no correspondence between latitudinal patterns of sea level anomaly and chlorophyll variance. This likely represents a transition from physical to biological control of the phytoplankton distribution.

Distributions and Variability of Particulate Organic Matter in a Coastal Upwelling System

In this study we examined the spatial and temporal variability of particulate organic material (POM) off Oregon during the upwelling season. High-resolution vertical profiling of beam attenuation was conducted along two cross-shelf transects. One transect was located in a region where the shelf is relatively uniform and narrow (off Cascade Head (CH)); the second transect was located in a region where the shelf is shallow and wide (off Cape Perpetua (CP)). In addition, water samples were collected for direct analysis of chlorophyll, particulate organic carbon (POC), and particulate organic nitrogen (PON). Beam attenuation was highly correlated with POC and PON. Striking differences in distribution patterns and characteristics of POM were observed between CH and CP. Off CH, elevated concentrations of chlorophyll and POC were restricted to the inner shelf and were highly variable in time. The magnitude of the observed short-term temporal variability was of the same order as that of the seasonal variability reported in previous studies. Elevated concentrations of nondegraded chlorophyll and POM were observed near the bottom. Downwelling and rapid sinking are two mechanisms by which phytoplankton cells can be delivered to the bottom before being degraded. POM may be then transported across the shelf via the benthic nepheloid layer. Along the CP transect, concentrations of POM were generally higher than they were along the CH transect and extended farther across the shelf. Characteristics of surface POM, namely, C: N ratios and carbon: chlorophyll ratios, differed between the two sites. These differences can be attributed to differences in shelf circulation.