Primary production in the eastern tropical Pacific: A review

The eastern tropical Pacific includes 28 million km² of ocean between 23.5°N and S and Central/South America and 140°W, and contains the eastern and equatorial branches of the north and South Pacific subtropical gyres plus two equatorial and two coastal countercurrents. Spatial patterns of primary production are in general determined by supply of macronutrients (nitrate, phosphate) from below the thermocline. Where the thermocline is shallow and intersects the lighted euphotic zone, biological production is enhanced. In the eastern tropical Pacific thermocline depth is controlled by three interrelated processes: a basin-scale east/west thermocline tilt, a basin-scale thermocline shoaling at the gyre margins, and local wind-driven upwelling. These processes regulate supply of nutrient-rich subsurface waters to the euphotic zone, and on their basis we have divided the eastern tropical Pacific into seven main regions. Primary production and its physical and chemical controls are described for each.Enhanced rates of macronutrient supply maintains levels of primary production in the eastern tropical Pacific above those of the oligotrophic subtropical gyres to the north and south. On the other hand lack of the micronutrient iron limits phytoplankton growth (and nitrogen fixation) over large portions of the open-ocean eastern tropical Pacific, depressing rates of primary production and resulting in the so-called high nitrate-low chlorophyll condition. Very high rates of primary production can occur in those coastal areas where both macronutrients and iron are supplied in abundance to surface waters. In these eutrophic coastal areas large phytoplankton cells dominate; conversely, in the open-ocean small cells are dominant. In a ‘shadow zone’ between the subtropical gyres with limited subsurface ventilation, enough production sinks and decays to produce anoxic and denitrified waters which spread beneath very large parts of the eastern tropical Pacific.Seasonal cycles are weak over much of the open-ocean eastern tropical Pacific, although several eutrophic coastal areas do exhibit substantial seasonality. The ENSO fluctuation, however, is an exceedingly important source of interannual variability in this region. El Niño in general results in a depressed thermocline and thus reduced rates of macronutrient supply and primary production. The multi-decadal PDO is likely also an important source of variability, with the ‘El Viejo’ phase of the PDO resulting in warmer and lower nutrient and productivity conditions similar to El Niño.On average the eastern tropical Pacific is moderately productive and, relative to Pacific and global means, its productivity and area are roughly equivalent. For example, it occupies about 18% of the Pacific Ocean by area and accounts for 22–23% of its productivity. Similarly, it occupies about 9% of the global ocean and accounts for 10% of its productivity. While representative, these average values obscure very substantial spatial and temporal variability that characterizes the dynamics of this tropical ocean.     

Open registers: past, present and future

The debate about open registers (ORs) is not a new matter, and throughout centuries States have taken advantage of other flags for their own profit in order to overcome any kind of restrictions. To understand this system in depth it is necessary to know about its origins, development and consolidation. Eradicating substandard registers calls for the application of specific directions like the ones presented, which are a result of many years of researching and working for international organizations aiming at the modernization and consolidation of some ORs. This has led to an increase in the levels of safety and credibility of the maritime administrations where they were applied.     

On the vertical distribution of

The aim of this paper is to present an analytical expression for the vertical distribution of the correlation between the horizontal ( ) and vertical ( ) wave velocity components. This quantity, , which appears explicitly in the time-averaged momentum balance equations, has been shown to play an important role in the vertical distribution of wave-induced currents.The proposed formulation for is based on an identity that relates the effective (wave) shear stress to the effective (wave) normal stresses ( ² and ²) and to the vorticity of the oscillatory flow gw. This general expression has been applied to simplified situations and has been shown to degenerate into other existing formulations with comparable simplifying assumptions, viz. irrotational waves in shallow water over an arbitrary bottom topography and breaking waves over a horizontal bottom.The model has also been applied to the case of waves interacting with a depth-varying current over a horizontal bottom, in which preliminary results have been obtained for a simplified situation invoking linear (small-amplitude) wave theory.     

Factors affecting spatial and temporal variability in material exchange between the Southern Everglades wetlands and Florida Bay (USA)

Physical and biological processes controlling spatial and temporal variations in material concentration and exchange between the Southern Everglades wetlands and Florida Bay were studied for 2.5 years in three of the five major creek systems draining the watershed. Daily total nitrogen (TN), and total phosphorus (TP) fluxes were measured for 2 years in Taylor River, and ten 10-day intensive studies were conducted in this creek to estimate the seasonal flux of dissolved inorganic nitrogen (N), phosphorus (P), total organic carbon (TOC), and suspended matter. Four 10-day studies were conducted simultaneously in Taylor, McCormick, and Trout Creeks to study the spatial variation in concentration and flux. The annual fluxes of TOC, TN, and TP from the Southern Everglades were estimated from regression equations. The Southern Everglades watershed, a 460-km² area that includes Taylor Slough and the area south of the C-111 canal, exported 7.1 g C m⁻², 0.46 g N m⁻², and 0.007 g P m⁻², annually. Everglades P flux is three to four orders of magnitude lower than published flux estimates from wetlands influenced by terrigenous sedimentary inputs. These low P flux values reflect both the inherently low P content of Everglades surface water and the efficiency of Everglades carbonate sediments and biota in conserving and recycling this limiting nutrient. The seasonal variation of freshwater input to the watershed was responsible for major temporal variations in N, P, and C export to Florida Bay; approximately 99% of the export occurred during the rainy season. Wind-driven forcing was most important during the later stages of the dry season when low freshwater head coincided with southerly winds, resulting in a net import of water and materials into the wetlands. We also observed an east to west decrease in TN:TP ratio from 212:1 to 127:1. Major spatial gradients in N:P ratios and nutrient concentration and flux among the creek were consistent with the westward decrease in surface water runoff from the P-limited Everglades and increased advection of relatively P-rich Gulf of Mexico (GOM) waters into Florida Bay. Comparison of measured nutrient flux from Everglades surface water inputs from this study with published estimates of other sources of nutrients to Florida Bay (i.e. atmospheric deposition, anthropogenic inputs from the Florida Keys, advection from the GOM) show that Everglades runoff represents only 2% of N inputs and 0.5% of P input to Florida Bay.     

Sediment Organic Carbon in Todos Santos Bay, Baja California, Mexico

Sediment grain size and organic carbon (OC) data collected over the past 50 years, together with δ¹³C values of OC in recently collected samples, were analyzed to improve understanding of sediment OC distribution and abundance in Todos Santos Bay. Sediments in the submarine canyon at the mouth of the bay and in quiet-water locations along the shore are fine grained, high in OC, and have generally low δ¹³C values; sediments in high-energy environments are low in OC and have high δ¹³C values. A bivariate isotopic mixing model indicates that none of the sediments contain >50% terrigenous OC (average ~30%), and that the terrigenous OC content of the sediments is a small proportion of the OC content of local soils. Sediment OC composition is apparently controlled by energy-related sorting and deposition, oxidation of much of the original terrigenous OC, and replacement of some terrigenous OC by marine OC.     

A search for natural or artificial objects located at the Earth-Moon libration points

Photographs in the vicinity of the Earth-Moon triangular libration points L4 and L5, and of the solar-synchronized positions in the associated halo orbits (A. A. Kamel, 1969, Ph.D. dissertation, Stanford University), were made during August–September 1979, using the 30-in Cassegrain telescope at Leuschner Observatory, Lafayette, California. An effective 2° square field was covered at each position. No discrete objects, either natural or artificial, were found. The detection limit was about 14th magnitude. The present work extends traditional SETI observations to include the search for interstellar probes (R. A. Freitas, Jr., 1980a, J. Brit. Interplanet. Soc.33, 95–100).