Observations of 13 C and Cd/Ca from benthic foraminifera have been interpreted to reflect a shoaling of northern source waters by about 1000 m during the Last Glacial Maximum, with the degree of shoaling being significant enough for the water mass to be renamed Glacial North Atlantic Intermediate Water. These nutrient tracers, however, may not solely reflect changes in water mass distributions. To quantify the distribution of Glacial North Atlantic Water, we perform a glacial water mass decomposition where the sparsity of data, geometrical constraints, and nonconservative tracer effects are taken into account, and the extrapolation for the unknown water mass end-members is guided by the modern-day circulation. Under the assumption that the glacial sources of remineralized material are similar to that of the modern day, we find a steady solution consistent with 241 13 C, 87 Cd/Ca, and 174 18 O observations and their respective uncertainties. The water mass decomposition indicates that the core of Glacial North Atlantic Water shoals and southern source water extends in greater quantities into the abyssal North Atlantic, as previously inferred. The depth of the deep northern-southern water mass interface and the volume of North Atlantic Water, however, are not grossly different from that of the modern day. Under this scenario, the vertical structure of glacial 13 C and Cd/Ca is primarily due to the greater accumulation of nutrients in lower North Atlantic Water, which may be a signal of the hoarding of excess carbon from the atmosphere by the glacial Atlantic.

A number of previous observational studies have found that the waters of the deep Pacific Ocean have an age, or elapsed time since contact with the surface, of 700-1000 yr. Numerical models suggest ages twice as old. Here, the authors present an inverse framework to determine the mean age and its upper and lower bounds given Global Ocean Data Analysis Project (GLODAP) radiocarbon observations, and they show that the potential range of ages increases with the number of constituents or sources that are included in the analysis. The inversion requires decomposing the World Ocean into source waters, which is obtained here using the total matrix intercomparison (TMI) method at up to 28 3 28 horizontal resolution with 11 113 surface sources. The authors find that the North Pacific at 2500-m depth can be no younger than 1100 yr old, which is older than some previous observational estimates. Accounting for the broadness of surface regions where waters originate leads to a reservoir-age correction of almost 100 yr smaller than would be estimated with a two or three water-mass decomposition and explains some of the discrepancy with previous observational studies. A best estimate of mean age is also presented using the mixing history along circulation pathways. Subject to the caveats that inference of the mixing history would benefit from further observations and that radiocarbon cannot rule out the presence of extremely old waters from exotic sources, the deep North Pacific waters are 1200-1500 yr old, which is more in line with existing numerical model results.

Westerly wind bursts (WWBs) in the equatorial Pacific are known to play a significant role in the development of El Niño events. They have typically been treated as a purely stochastic external forcing of ENSO. Recent observations, however, show that WWB characteristics depend upon the large-scale SST field. The consequences of such a WWB modulation by SST are examined using an ocean general circulation model coupled to a statistical atmosphere model (i.e., a hybrid coupled model). An explicit WWB component is added to the model with guidance from a 23-yr observational record. The WWB parameterization scheme is constructed such that the likelihood of WWB occurrence increases as the western Pacific warm pool extends: a “semistochastic” formulation, which has both deterministic and stochastic elements. The location of the WWBs is parameterized to migrate with the edge of the warm pool. It is found that modulation of WWBs by SST strongly affects the characteristics of ENSO. In particular, coupled feedbacks between SST and WWBs may be sufficient to transfer the system from a damped regime to one with self-sustained oscillations. Modulated WWBs also play a role in the irregular timing of warm episodes and the asymmetry in the size of warm and cold events in this ENSO model. Parameterizing the modulation of WWBs by an increase of the linear air–sea coupling coefficient seems to miss important dynamical processes, and a purely stochastic representation of WWBs elicits only a weak ocean response. Based upon this evidence, it is proposed that WWBs may need to be treated as an internal part of the coupled ENSO system, and that the detailed knowledge of wind burst dynamics may be necessary to explain the characteristics of ENSO.

Ocean tracer distributions have long been used to decompose the deep ocean into constituent water masses, but previous inverse methods have generally been limited to just a few water masses that have been defined by a subjective choice of static property combinations. Through air-sea interaction and upper-ocean processes, all surface locations are potential sources of distinct tracer properties, and thus it is natural to define a distinct water type for each surface site. Here, a new box inversion method is developed to explore the contributions of all surface locations to the ocean interior, as well as the degree to which the observed tracer fields can be explained by a steady-state circulation with unchanging surface-boundary conditions. The total matrix intercomparison (TMI) method is a novel way to invert observations to solve for the pathways connecting every surface point to every interior point. In the limiting case that the circulation is steady and that five conservative tracers are perfectly observed, the TMI method unambiguously recovers the complete pathways information, owing to the fact that each grid box has, at most, six neighbors. Modern-day climatologies of temperature, salinity, phosphate, nitrate, oxygen, and oxygen-18/oxygen-16 isotope ratios are simultaneously inverted at 48 3 48 grid resolution with 33 vertical levels. Using boundary conditions at the surface and seafloor, the entire interior distribution of the observed tracers is reconstructed using the TMI method. Assuming that seafloor fluxes of tracer properties can be neglected, the method suggests that 25% or less of the water residing in the deep North Pacific originated in the North Atlantic. Integrating over the global ocean, the Southern Ocean is dominant, as the inversion indicates that almost 60% of the ocean volume originates from south of the Southern Hemisphere subtropical front.