In the Antarctic Zone of the Southern Ocean, the coupled observations of elevated diatom-bound 15 N/ 14 N (δ 15 N db ) and reduced export production during the ice ages indicates more complete nitrate (NO 3 − ) consumption. This evidence points to an ice age decline in gross NO 3 − supply from the deep ocean to the surface wind-mixed layer, which…

Nitrogen and oxygen isotopes of NO3- have been measured in snow and firn from Summit, Greenland. The 15N/ 14N and 18O/16O ratios of NO 3- in recently fallen snow are similar to those of surface snow. Diurnal variation is observed in 15N/ 14N of NO3-, and possibly 18O/16O, suggesting fractionating loss of NO3- from snow during the day, which is…

We report measurements of the δ15N of nitrate, suspended particulate nitrogen (PN), and sinking PN from cruises and moored sediment traps in the Subantarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia. As expected, surface water nitrate δ15N increased as nitrate was consumed during the spring/summer bloom. In contrast, the seasonal…

Severely negative 14C anomalies from the mid-depth Pacific and the Arabian Sea have been taken as support for the hypothesized deglacial release of a previously isolated, extremely 14C-deplete deep ocean carbon reservoir. We report box model simulations that cast doubt on both the existence of the hypothesized deep reservoir and its ability to…

Culture studies of denitrifying bacteria predict that denitrification will generate equivalent gradients in the δ15N and δ18O of deep ocean nitrate. A depth profile of nitrate isotopes from the Hawaii Ocean Time-series Station ALOHA shows less of an increase in δ18O than in δ15N as one ascends from abyssal waters into the denitrification-impacted…

The nitrogen isotope composition of diatom opal (δ15Ndb) is a valuable recorder of nitrate utilization in the polar surface oceans and a measure of the efficiency of the biological pump. Past down-core records of δ15Ndb involved the measurement of the biogenic opal fraction up to 150μm in size, which should represent the bulk of the preserved…

The Southern Ocean is widely recognized as a potential cause of the lower atmospheric concentration of CO2 during ice ages, but the mechanism is debated. Focusing on the Southern Ocean surface, we review biogeochemical paleoproxy data and carbon cycle concepts that together favor the view that both the Antarctic and Subantarctic Zones (AZ and SAZ)…

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean. Indeed, dust supply to the Southern Ocean increases during ice ages, and iron fertilizationg of the subantarctic zone may have contributed up to 40-parts per million…

Previous studies have suggested that during the late Pleistocene ice ages, surface-deep exchange was somehow weakened in the Southern Ocean s Antarctic Zone, which reduced the leakage of deeply sequestered carbon dioxide and thus contributed to the lower atmospheric carbon dioxide levels of the ice ages. Here, high-resolution diatom-bound nitrogen…

Previous studies suggest that meridional migrations of the Antarctic Circumpolar Current may have altered wind-driven upwelling and carbon dioxide degassing in the Southern Ocean during past climate transitions. Here, we report a quantitative and continuous record of the Antarctic Circumpolar Current latitude over the last glacial-interglacial…

Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the…

Nitrogen fixation is crucial for maintaining biological productivity in the oceans, because it replaces the biologically available nitrogen that is lost through denitrification. But, owing to its temporal and spatial variability, the global distribution of marine nitrogen fixation is difficult to determine from direct shipboard measurements. This…

Equatorial Pacific nitrate 15N/14N and 18O/16O (δ15N and δ18O) measurements from repeat station occupations are used to: (1) identify the source of surface waters, (2) estimate the nitrate assimilation isotope effect, (3) characterize the temporal relationship between the supply and consumption of nitrate in surface waters, and (4) quantify the…

We used the nitrogen isotope ratio of algae, suspended particles and nitrate in the water column to track spatial variations in the marine nitrogen cycle in the Mediterranean Sea. Surface PON (5-74 m) was more depleted in 15N in the eastern basin (-0.3±0.5‰) than in the western basin (+2.4±1.4‰), suggesting that nitrogen supplied by biological N2…

During the last interglacial period, global temperatures were ∼2°C warmer than at present and sea level was 6 to 8 meters higher. Southern Ocean sediments reveal a spike in authigenic uranium 127,000 years ago, within the last interglacial, reflecting decreased oxygenation of deep water by Antarctic Bottom Water (AABW). Unlike ice age reductions…

Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial-interglacial change in deep North Pacific phosphate (PO4) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive…

We report measurements of the nitrogen isotopic composition of nitrate (the δ 15N of NO 3 -) across the equatorial Pacific, for zonal transects from 165E to 95W and meridional transects across 95 and 110W. The δ 15N of NO 3 - is similar in the equatorial thermocline (100 m) and intermediate depth waters (150 to 600 m), averaging (7.1 0.3)‰ and (7…

Tropical forests account for one third of terrestrial primary production and contribute significantly to the land carbon sink 1,2. The future of this sink relies critically on forest interactions with nutrient cycles 3-5. Humid montane tropical forests are often thought to be rich in phosphorus, but to contain low levels of bioavailable nitrogen 6…

Phytoplankton in the Antarctic deplete silicic acid (Si(OH)4) to a far greater extent than they do nitrate (NO3-). This pattern can be reversed by the addition of iron which dramatically lowers diatom Si(OH)4:NO3- uptake ratios. Higher iron supply during glacial times would thus drive the Antarctic towards NO3- depletion with excess Si(OH)4…