摘要:

In this study we examine ENSO diversity in a 500 year control simulation of the National Center for Atmospheric Research (NCAR) Community Climate System Model version 4 (CCSM4), focusing on warm events. Standard and modified Niño3 and Niño4 indices are used to identify different event types. CCSM4 shows a rich diversity of El Niño flavors with characteristics that are comparable to what was found in observations, the SODA 2.0.2/3 ocean reanalysis, and the GFDL CM2.1 model, a climate model whose ENSO characteristics have been extensively analyzed. In agreement with previous studies available in the literature, warm events peaking in the central/western Pacific are characterized by wind stress and precipitation fields confined to the western side of the basin, and show weak or absent recharge/discharge thermocline processes. A heat budget analysis of four different El Niño flavors, peaking at different longitudes, confirms the leading role of the thermocline and zonal advective feedbacks in the Niño3 and Niño4 regions, respectively. However, the growth of events centered further west appears to be controlled by nonlinear zonal advection, a result that differs from what was found in the GFDL CM2.1 model, but that is consistent with some observational evi

ISSN:0148-0227    

DOI:10.1002/jgrc.20335

年代:2013

数据来源: WILEY

摘要:

In summer and autumn 2010, a highly anomalous phytoplankton bloom, with chlorophyll concentration more than double that of previous years, was observed in the Irminger Basin, southwest of Iceland. Two unusual events occurred during 2010 which had the potential to promote the unusual bloom. First, in spring 2010, the Eyjafjallajökull volcano in Iceland erupted, depositing large quantities of tephra into the subpolar North Atlantic. Second, during the winter of 2009/2010 the North Atlantic Oscillation (NAO) became extremely negative, developing into the second strongest negative NAO on record. Hydrographic conditions were highly anomalous in the region, with an influx of freshwater spreading through the basin, and unusual nutrient and mixed layer depth conditions. Here we use a combination of satellite, modeled and in situ data to investigate whether the input of iron from the volcanic eruption or change in hydrographic conditions due to the extreme negative NAO were responsible for the anomalous phytoplankton bloom. We conclude that changes in physical forcing driven by the NAO, and not the volcanic eruption, stimulated the unusual bloom

ISSN:0148-0227    

DOI:10.1002/jgrc.20363

年代:2013

数据来源: WILEY

摘要:

The difference between nitrate δ15N and δ18O, or Δ(15–18), is sensitive to organic matter remineralization and tracks the modification of nitrate as it passes from the deep Pacific Ocean, through the Southern Ocean surface, and into the intermediate‐depth Pacific. Circumpolar Deep Water (CDW) is upwelled with a nitrate Δ(15–18) of +3.0‰ and appears unaltered by nitrate assimilation in the Antarctic surface. However, within Subantarctic Mode Water (SAMW)—the primary conduit of deep‐sea nutrients to the lower latitudes—nitrate δ15N and δ18O are both higher than CDW, while nitrate Δ(15–18) is as low as +1.5‰. The lower SAMW nitrate Δ(15–18) results from the production of low δ15N organic matter during partial assimilation of the surface nitrate pool followed by its sinking and remineralization back to nitrate, lowering the δ15N of thermocline nitrate more than its δ18O. As SAMW flows toward the lower latitudes, nitrate Δ(15–18) is expected and observed to increase because complete surface ocean nitrate consumption produces sinking nitrogen with a δ15N similar to that of the nitrate supplied from below such that remineralization lowers the δ18O of nitrate, but not its δ15N. Nitrate Δ(15–18) is also used to estimate a surprisingly high low latitude sinking nitrogen δ15N of ≈9.0‰, suggesting a major effect of14NO3−loss by tropical denitrification on middepth nitrate basin‐wide. The remineralization of this high sinking nitrogen δ15N increases nitrate Δ(15–18) as deep as the southward‐moving Pacific Deep Water, which supplies CDW. This relatively high Δ(15–18) is then lowered to the observed CDW value by the reminerali

ISSN:0148-0227    

DOI:10.1002/jgrc.20316

年代:2013

数据来源: WILEY

摘要:

The study of air‐sea CO2fluxes (FCO2) in the coastal region is needed to better understand the processes that influence the direction and magnitude ofFCO2and to constrain the global carbon budget. We implemented a 1 year (January through December 2009) paired study to measureFCO2in the intertidal zone (the coastline to 1.6 km offshore) and the near‐shore (∼3 km offshore) off the north‐western coast of Baja California (Mexico); a region influenced by year‐round upwelling.FCO2was determined in the intertidal zone via eddy covariance; while in the near‐shore using mooring buoy sensors then calculated with the bulk method. The near‐shore region was a weak annual net source of CO2to the atmosphere (0.043 mol CO2m−2y−1); where 91% of the outgassedFCO2was contributed during the upwelling season. Sea surface temperature (SST) and ΔpCO2(from upwelling) showed the strongest relationship withFCO2in the near‐shore, suggesting the importance of meso‐scale processes (upwelling).FCO2in the intertidal zone were up to four orders of magnitude higher thanFCO2in the near‐shore. Wind speed showed the strongest relationship withFCO2in the intertidal zone, suggesting the relevance of micro‐scale processes. Results show that there are substantial spatial and temporal differences inFCO2between the near‐shore and intertidal zone; likely a result of heterogeneity. We suggest that detailed spatial and temporal measurements are needed across the coastal oceans and continental margins to better understand the mechanisms which controlFCO2, as well as reduce uncertainties and constrain regional and

ISSN:0148-0227    

DOI:10.1002/jgrc.20319

年代:2013

数据来源: WILEY

摘要:

The three‐dimensional structure and the origin of mesoscale anticyclonic intrathermocline eddies (ITEs) in the coastal transition zone (CTZ) off central Chile (31–41°S) were analyzed through the combination of data from oceanographic cruises and satellite altimetry, and the application of an eddy‐resolving primitive equation ocean model coupled with a numerical experiment using a passive tracer. In this region, ITEs are represented by subsurface lenses (∼100 km diameter; 500 m thickness or vertical extension) of nearly homogeneous salinity (>34.5) and oxygen‐deficient (<1.0 mL L−1) waters, properties which are linked to the equatorial subsurface water mass (ESSW) transported poleward by the Peru‐Chile undercurrent (PCUC) in the coastal band. At least five to seven ITEs were observed simultaneously in the area between 31° and 38°S during winter cruises in 1997 and 2009. Satellite data indicated that the ITEs identified from in situ data moved westward, each at a mean speed of ∼2 km d−1and transported a total volume of ∼1 × 106m3s−1(=1 Sv); the lifespan of each ITE ranged from a few months to 1 year. Model results indicate that ITEs become detached from the PCUC under summer upwelling condi

ISSN:0148-0227    

DOI:10.1002/jgrc.20337

年代:2013

数据来源: WILEY

摘要:

Physical and biogeochemical processes determining the distribution, transport, and fate of nutrients delivered by the Mississippi and Atchafalaya river basin (MARB) to the inner Louisiana continental shelf (LCS) were examined using a three‐dimensional hydrodynamic model and observations of hydrography, nutrients, and organic carbon collected during 12 cruises. Two aspects of nutrient transport and fate on the inner LCS (<50 m depth) were evaluated: (1) along‐shelf and cross‐shelf transports were calculated and (2) nutrient sinks and sources were inferred. On average, 47% of the lower Mississippi River freshwater traveled westward on the LCS, but this percentage was reduced during summer when currents reversed to a predominately upcoast direction. Changes from mainly inorganic to organic nutrients were observed at salinity between 20 and 30, and above 30, organic nutrients were the dominant forms. Westward transport of dissolved inorganic nitrogen (DIN) was about 25% of the combined DIN load from the MARB, whereas westward transport of dissolved organic nitrogen (DON) was 2.8‐fold larger than the MARB DON load. Different from dissolved inorganic nutrients, for which the rivers were the primary source, the dominant source of organic nutrients was advection from offshore. Overall, the inner LCS was estimated to be a net sink for total nitrogen in the amount of −3.14 mmol N m−2d−1and a net sink for total phosphorus in the amount of −0.28 mmol P m−2d−1. These sinks were approximately 33% and 59% of the total N and P sources, respectivel

ISSN:0148-0227    

DOI:10.1002/jgrc.20362

年代:2013

数据来源: WILEY

摘要:

In the productive central‐Oregon coastal upwelling environment, wind‐driven upwelling, tides, and topographic effects vary across the shelf, setting the stage for varied biogeochemical responses to physical drivers. Current, temperature, salinity, and dissolved oxygen (DO) measurements from three moorings deployed during the upwelling seasons of 2009–2011 off the central‐Oregon coast are analyzed over three time bands (interannual, subtidal, tidal) to explore the relationship between mid (70 m) and inner‐shelf (15 m) upwelling dynamics and the associated effect on DO. Topographic effects are observed in each time band due to the Heceta and Stonewall Bank complex. Seasonal cumulative hypoxia (DO < 1.4 mL L−1) calculations identify two regions, a well‐ventilated inner shelf and a midshelf vulnerable to hypoxia (98 ± 15 days annually). On tidal timescales, along‐shelf diurnal (K1) velocities are intensified over the Bank, 0.08 m s−1compared with 0.03 m s−1to the north. Interannual variability in the timing of spring and fall transitions, defined using glider‐measured continental slope source water temperature, is observed on the midshelf. Interannual source water DO concentrations vary on the order of 0.1 mL L−1. Each spring and summer, DO decline rates are modulated by physical and biological processes. The net observed decrease is about 30% of the expected draw down due to water‐column respiration. Physical processes initiate low‐oxygen conditions on the shelf through coastal upwelling and subsequently prevent the system via advection and mixing from reaching the potential anoxic levels anti

ISSN:0148-0227    

DOI:10.1002/jgrc.20361

年代:2013

数据来源: WILEY

摘要:

Submarine canyons are sites of intense turbulence and mixing. Monterey Canyon cuts into the continental shelf off California, and is defined by its sinuous nature. Temperature, salinity, and current velocity measurements were made over 21 days in April 2009 with a depth‐cycling towed body to understand internal tide propagation and dissipation through the canyon bends. Cross‐canyon transects reveal complex flow patterns that follow large‐scale bathymetry on scales greater than 5 km. Changes in thalweg direction deflect baroclinic energy flux, but the bends in the measurement region are too sharp for the flux to follow the thalweg. Ridges that form the bends in the canyon act as obstacles to the flow, and turbulent dissipation rates greater than 1 × 10−5m2s−3were observed on their flanks, especially at the largest meander (the Gooseneck). The canyon‐integrated baroclinic energy flux increased from 2.7 MW at the most western section to 3.7 MW at the Gooseneck Ridge, which has a nearly critical bottom slope with respect to the semidiurnal baroclinic tide on the western side; baroclinic energy flux was 50% less on the eastern side of the ridge. While measured dissipation near the Gooseneck Meander was sufficient to explain the flux divergence, turbulence near the Gooseneck may have been undersampled. Between the Gooseneck Ridge and the most eastern cross‐canyon transect, dissipation may account for the decrease in the energy flux; though a local energy balance does not hold, the energy budget is balanced over the larger scale of the measurement region east of the G

ISSN:0148-0227    

DOI:10.1002/jgrc.20368

年代:2013

数据来源: WILEY

摘要:

Bottom water exchange between the Japan and Yamato Basins in the abyssal Japan Sea is investigated based on data from two research cruises in June 2010 and June 2011. Distributions of water properties and velocity profiles from CTD/LADCP observations revealed a two‐layer water mass exchange in a rotating system. The cold Japan Basin Bottom Water (JBBW) with high dissolved oxygen (DO) concentrations flowed into the Yamato Basin along the northern boundary of the channel connecting the basins, while the warmer, lower‐DO Yamato Basin Bottom Water (YBBW) extended over the JBBW along the southern periphery of the channel. A benthic front between the JBBW and YBBW was observed in both cruises, though the front shifted to the northeast in 2011 compared with its 2010 location. Further, the bottom flows in the channel were not unidirectional in 2011, though consistent southwestward flows were observed in 2010. The JBBW transport into the Yamato Basin was also larger in 2010 than in 2011. Analysis of historical hydrographic data showed that the benthic front exists mostly in the narrowest region of the channel, though it fluctuates temporarily to the northeast or southwest. The fluctuation of the benthic front appears to be associated with the JBBW transport because the observations in June 2010 and June 2011 were carried out during periods of southwestward extension of cold water and northeast protrusion of warm water, respectively. A relationship between benthic front displacements and mesoscale warm eddy migrations is sugges

ISSN:0148-0227    

DOI:10.1002/jgrc.20373

年代:2013

数据来源: WILEY

摘要:

Ocean bottom pressure (OBP) variability in the region of the Agulhas Current off the South African coast is a crucial variable in the understanding of dynamic processes in the ocean, but measurements currently available lack either precision or spatial and temporal coverage. We provide a quantitative estimate of OBP variability throughout the region with the help of a setup of the ROMS regional ocean model. Driving the model with boundary conditions from a global ocean model and atmospheric reanalysis data and running it for 8 years, we are able to reproduce many characteristic properties of the regional ocean circulation visible in sea surface height and OBP fields. While the in situ pressure‐inverted echo sounders (PIES) measuring local OBP variations on short time scales are sparse in the region, our model provides a comprehensive estimate of OBP variations throughout the region which reach values of up to 15 hPa when barotropic Agulhas rings reach the Cape Basin. These signals turn out to be difficult to measure with current gravimetry solutions from the GRACE satellites, but estimates of localized noise levels for a GRACE follow‐on mission let the search for them in future satellite measurements appear via

ISSN:0148-0227    

DOI:10.1002/jgrc.20372

年代:2013

数据来源: WILEY