Latitudinal distribution of mesozooplankton in the off-equatorial northeastern Pacific before and after the 1998/99 La Niña event

Factors affecting mesozooplankton distributions in the northeastern tropical Pacific Ocean were investigated using data obtained along a meridian line (5 degrees -12 degrees N, 131.5 degrees W) in the summers of 1998, 1999, and 2003. The survey periods corresponded to a sharp transition between the 1997-1998 El Ni?o and 1998-1999 La Ni?a events, the 1999 La Ni?a event, and near-normal conditions after the moderate 2002-2003 El Ni?o in the equatorial Pacific. A strong upwelling in the divergence zone from 10.5 degrees to 11 degrees N caused a shoaling of the thermocline depth (approximately 30 m), resulting in increases in nitrate and phytoplankton chlorophyll a (chl-a) concentrations, and, in turn, mesozooplankton abundance during the La Ni?a in 1999. In contrast, in 1998, remnants of El Ni?o characteristics, deeper thermocline depth (60-150 m) and warm surface water (>28 degrees C), led to low concentrations of nitrate, chl-a and low mesozooplankton abundance, except in the convergence zone around 7 degrees N. The thermocline depth and nitrate concentration obtained during the near-normal period in 2003 corresponded to intermediate values as compared to those obtained during El Ni?o and La Ni?a conditions. Interannual changes in the position and strength of ecotones, such as divergence and convergence zones, affected mesozooplankton community structure and cyclopoid-to-calanoid ratios along the 131.5 degrees W meridian line. The clustering pattern of the mesozooplankton community was mostly characterized by calanoid (mainly Clausocalanus sp.) and cyclopoid (mainly Oncaea sp.) copepods, accounting for most of the observed differences among groups during the study period. Cyclopoids and calanoids were more abundant in 1999 than in 1998 or 2003, with a sharp increase to the north, while they were less abundant to the north in 1998 and 2003. The cyclopoid-to-calanoid ratio peaked in the convergence zone in 1998 and the divergence zones in 1999 and 2003, apparently due to the strength and location of the ecotones. Principal component analysis (PCA) with environmental factors and dominant mesozooplankton groups showed that dominant groups were affected by nitrate and chl-a concentrations in 1998, by sigma-t (water density), nitrate and chl-a concentrations in 1999, and by sigma-t, salinity and chl-a concentration (except siphonophores) in 2003. Latitudinal distribution of thermocline depth before and after the 1998/99 La Ni?a event showed a distinct interannual difference. The abundance of mesozooplankton in the divergence zone in 1999 was distinctively higher than abundances found in the convergence and divergence zones in 1998 and 2003, which resulted from the shallow thermocline depth due to an intensified upwelling during the strong 1998-1999 La Ni?a event.     

Detecting the intertidal morphologic change using satellite data

Previous research has suggested that competitive bottlenecks may exist for the Mediterranean grey mullets (Osteichthyes, Mugilidae) at the fry stage with the exotic Cyprinus carpio (Osteichthyes, Cyprinidae) playing a central role. As a consequence, the structure of grey mullet assemblages at later stages is thought to reflect previous competition as well as differences in osmoregulatory skills. This paper tests that hypothesis by examining four predictions about the relative abundance of five grey mullet species in 42 Western Mediterranean estuary sites from three areas (Aiguamolls de l'Empordà, Ebro Delta and Minorca) differing in the salinity level and occurrence of C. carpio. Field data confirmed the predictions as: (1) Liza aurata and Mugil cephalus were scarce everywhere and never dominated the assemblage; (2) Liza saliens dominated the assemblage where the salinity level was higher than 13; (3) Liza ramado always dominated the assemblage where the salinity level was lower than 13 and C. carpio was present; and (4) Chelon labrosus dominated the assemblage only where the salinity level was lower than 13 and C. carpio was absent. The catch per unit effort of C. labrosus of any size was smaller in the presence of C. carpio than where it had not been introduced, which is in agreement with the juvenile competitive bottleneck hypothesis. Discriminant analysis confirmed that the assemblage structure was linked to the salinity level and the occurrence of C. carpio for both early juveniles and late juveniles as well as adults. The data reported here reveal that the structure of grey mullet assemblages inhabiting Mediterranean estuaries is determined by salinity and competitive interactions at the fry stage.     

The release of dissolved actinium to the ocean: A global comparison of different end-members

The measurement of short-lived ²²³Ra often involves a second measurement for supported activities, which represents ²²⁷Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of ²²⁷Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles ²²⁷Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine end-members. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of ²²⁷Ac near its potential sources.The average ²²⁷Ac activities of nearshore marine end-members range from 0.4 dpm m^− 3 at the Gulf of Mexico to 3.0 dpm m^− 3 in the coastal waters of the Korean Strait. In analogy to ²²⁸Ra, we find the extension of adjacent shelf regions to play a substantial role for ²²⁷Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean ²²⁷Ac inventory of 1.35 * 10¹⁸ dpm ²²⁷Ac_ex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm m⁻² y^− 1 from the deep-sea floor. For the shelf regions, we obtain a global inventory of ²²⁷Ac of 4.5 * 10¹⁵ dpm, which cannot be converted directly into a flux value, as the regional loss term of ²²⁷Ac to the open ocean would have to be included.Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to ²³¹Pa_ex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released [Moore, W.S., Ussler, W. and Paull, C.K., 2008-this issue. Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge. Marine Chemistry]. Another potential mechanism of producing deviations in ²²⁷Ac/²²⁸Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including ²²⁷Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution.     

Aggregation of riverine colloidal iron in estuaries: A new kinetic study using stopped-flow mixing

The kinetics of aggregation of riverine colloidal iron have been examined using a stopped-flow technique which probes the first few seconds of mixing between river and sea water end members. A significant fraction, up to 80%, of the colloidal iron is aggregated during the first 1–2 s of mixing, indicating that the aggregation process is much faster than previously thought. Most of the aggregation induced by seawater results from the divalent cations Mg²⁺ and Ca²⁺, with the overall ionic strength having little influence. At equal concentrations of 27 mM, the rate of aggregation by alkaline earth cations increased with ionic size Mg²⁺ < Ca²⁺ < Sr²⁺ < Ba²⁺. The aggregation rates were indifferent to the anion (Cl⁻ or SO₄²⁻) present. Very high aggregation rates were also induced by the common water treatment coagulant Al₂(SO₄)₃ at concentrations in the range 20–30 µM Al(III), several orders of magnitude lower that those used for the seawater cations. Our results support the view that specific chemical interactions between the cations and the colloid particle surface, rather than simple electrical effects, control the colloid stability.     

Storm surge simulation using wind-wave-surge coupling model

Simulation of a storm surge caused by Typhoon 9918 in the Yatsushiro Sea, Kyushu, Japan was hindcasted by the synchronous coupled wind-wave-surge model composed of a Meso-scale meteorological model (MM5) for the wind and sea surface pressure, a spectral third-generation wind-wave model (Wavewatch III) for waves, and the coastal ocean model (Princeton Ocean Model). Inclusion of the whitecap wave breaking stresses (whitecap dissipation stress) in the coastal ocean model made it possible to reproduce the extreme surge height in the extremely shallow bay.     

VR c photometry of dwarf cepheids (I)

In this paper, we present VRc photometric observations of four dwarf cepheids: YZ Boo (P = 0 _. ^d 104, V = 0 _. ^m 5), AD CMi (P = 0 _. ^d 123, V = 0 _. ^m 5), XX Cyg (P = 0 _. ^d 135, V = 0 _. ^m 5), EH Lib (P = 0 _. ^d 088, V = 0 _. ^m 7). The light curves were obtained at West Mountain Observatory, Provo, Utah on 14 nights from 1983 through 1986 and contain 589 data points in each of theV andR bands in the Cousin photometric system. A detailed study of these stars, based on the present light curves, will be published separately.     

Radiative effect of black carbon aerosol on seasonal variation in snow depth in the Northern-Hemisphere

In this research, we studied the effects of black carbon (BC) aerosol radiative forcing on seasonal variation in the Northern Hemisphere (NH) using numerical simulations with the NASA finite-volume General Circulation Model (fvGCM) forced with monthly varying three-dimensional aerosol distributions from the Goddard Ozone Chemistry Aerosol Radiation and Transport Model (GOCART). The results show that atmospheric warming due to black carbon aerosols subsequently warm the atmosphere and land surfaces, especially those over Eurasia. As a result, the snow depth in Eurasia was greatly reduced in late winter and spring, and the reduction in snow cover decreased the surface albedo. Our surface energy balance analysis shows that the surface warming due to aerosol absorption causes early snow melting and further increases surface-atmosphere warming through snow/ice albedo feedback. Therefore, BC aerosol forcing may be an important factor affecting the snow/ice albedo in the NH.     

Simulation of snowstorm over the Yellow Sea using a mesoscale coupled model

This study aims to examine the favorable conditions for an ocean effect snowstorm across the Yellow Sea over the southwestern coast of Korea on 21 December 2005, using a coupled model with a Coupled Ocean/Atmosphere Mesoscale Prediction System as the atmospheric component and the Regional Ocean Modeling System as the oceanic component. Simulation of heavy snowfall event, which was 44.3 cm of snow accumulated in 24-hour, was performed to investigate the mesoscale structure, dynamics and development mechanisms in the snowstorm. As a result from 48-hour integration, the results of simulation showed that barotropic instability and turbulent heat fluxes played important roles in the formation of snowstorm. The enhanced surface diabatic heating was dominant in the latent heat flux, and eventually induced convective instability. An additional factor was the favorable condition of synoptic environment, accessing the cold air transport by the approach of the upper-level cold vortex over the warm ocean. Besides these factors, conditional symmetric instability (CSI) is a mechanism which can result in a heavy snowfall with sufficient moisture and upward vertical motion. A slantwise convection from the release of CSI could support a complex snowfall event with heavier than expected amounts. The result comparison between a coupled model and an uncoupled model supports that airsea coupling has an impact of decreasing of about 10% in a snowfall amount on the snowstorm.     

How do weather characteristics change in a warming climate?

The possible change in the characteristics of weather in the future should be considered as important as the mean climate change because the increasing risk of extremes is related to the variability on daily time scales. The weather characteristics can be represented by the climatological mean interdiurnal (day-to-day) variability (MIDV). This paper first assessed the phase five of the Coupled Model Intercomparison Project coupled climate models’ capability to represent MIDV for the surface maximum and minimum temperature, surface wind speed and precipitation under the present climate condition. Based on the assessment, we selected three best models for projecting future change. We found that the future changes in MIDV are characterized by: (a) a marked reduction in surface maximum and minimum temperature over high latitudes during the cold season; (b) a stronger reduction in the surface minimum temperature than in the maximum temperature; (c) a reduction in surface wind speed over large parts of lands in Northern Hemisphere (NH) during NH spring; (d) a noticeable increase in precipitation in NH mid-high latitudes in NH spring and winter, and in particular over East Asia throughout most of the year.