The relative abundance of diatom taxa in 216 core tops has been quantified and compared, using cluster analysis, with assemblages in six cores located beneath different water masses of the North Pacific Ocean. All but one sequence span at least 1.5 m.y., (early Pleistocene to Holocene), and one extends to 2.6 Ma. The quantitative abundance of each taxon and the space-time occurrence of each cluster are interpreted as tracers of oceanographic conditions. In addition to high-frequency (glacial-interglacial) oscillations, the records display rapid steplike changes at 2.4 Ma, 1.6–1.5 Ma, 1.0 Ma, 0.8–0.7 Ma, and 0.35 Ma. Two secondary transitions, recorded only in the northwestern cores, occur at 2.0 Ma and 1.1 Ma. We conclude that both the high-frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses, under the influence of the Siberian high-pressure and Aleutian low-pressure atmospheric cells. We further conclude that (1) the subarctic water mass has developed progressively and attained its modern structure only in the late Pleistocene; (2) some stages of this evolution may have occurred earlier in the eastern subarctic; (3) the Holocene is an atypical “warm” extreme, so that the present is not a very good key to the past; (4) there were several glaciations between 2.4 and 2.0 Ma; and (5) the Subtropical Gyre is more conservative than the Subarctic Gyre, and major changes in the region have been due to forcing from the north. We propose a conceptual model of oscillating metastable climatic modes, maintained by internal feedback; and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded.

Pliocene‐Pleistocene evolution of the North Pacific Ocean‐Atmosphere system, interpreted from fossil diatoms

Research during the last 15 years has shown that there is order in large-scale air-sea interactions, so that space scales of abnormalities of the lower atmosphere's circulation and the upper oceanic thermal structure are comparable. Because of this air-sea coupling, each oceanic or atmospheric pattern can be reasonably well specified by the other. Patterns of oceanic thermal anomalies are about an order of magnitude more persistent than those of atmospheric circulations, and empirical studies have had some success in using sea surface temperature patterns in long-range weather prediction. In addition to empirical studies, efforts continue in the development of numerical-dynamical models in order to understand the complex linkages of the large-scale air-sea system.

https://science.sciencemag.org/content/sci/214/4523/869.full.pdf

Large-scale air-sea interactions and short-period climatic fluctuatioins.

North Atlantic synoptic-scale processes are analyzed by bandpassing 6-hourly NCEP–NCAR reanalysis data (1958–98) for several synoptic ranges corresponding to ultrahigh-frequency variability (0.5–2 days), synoptic-scale variability (2–6 days), slow synoptic processes (6–12 days), and low-frequency variability (12–30 days). Climatological patterns of the intensity of synoptic processes are not collocated for different ranges of variability, especially in the lower troposphere. Intensities of synoptic processes demonstrate opposite trends between the North American coast and in the northeast Atlantic. Although north of 40°N the intensity of ultrahigh-frequency variability and synoptic-scale processes show similar interannual variability, further analysis indicates that secular changes, and decadal-scale and interannual variability in the intensities of synoptic processes may not be necessarily consistent for different synoptic timescales. Magnitudes of winter ultrahigh-frequency variability are high...

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Climatology and Interannual Variability in the Intensity of Synoptic-Scale Processes in the North Atlantic from the NCEP–NCAR Reanalysis Data

Synoptic-scale variability in the air‐sea turbulent fluxes in the areas of midlatitudinal western boundary currents is analyzed. In the Gulf Stream area, ocean‐atmosphere fluxes on synoptic time- and space scales are clearly coordinated with the propagating synoptic-scale atmospheric transients. The statistical analysis of 6-hourly resolution sea level pressure and surface turbulent fluxes from the NCEP‐NCAR reanalysis for the period from 1948 to 2000 in the area of strong sea surface temperature gradients in the Gulf Stream gives strong proof for the association between the propagating cyclones and synoptic patterns of surface turbulent fluxes. It is shown that sea‐air interaction in this area is controlled by the sharpness of surface temperature gradients in the ocean and by the intensity of the advection of the air masses in different parts of cyclones during the cold-air and warm-air outbreaks. A simple parameter based on the joint consideration of the characteristics of sea surface temperature and sea level pressure fields is used to characterize the synoptic variability of air‐sea turbulent fluxes. The effectiveness of the relationship between surface temperature and surface pressure on one side and air‐sea flux anomalies on the other vary from year to year in phase with variability in the frequencies of deep atmospheric cyclones in the Gulf Stream area. The limits of applicability of the approach, its sensitivity to higher-resolution sea surface temperature data, and the possibility of its further applications are discussed.

/pdf/synoptic-variability-of-ocean-atmosphere-turbulent-fluxes-yloi6ghg6e.pdf

Synoptic Variability of Ocean-Atmosphere Turbulent Fluxes Associated with Atmospheric Cyclones

Synoptic variability of ocean-atmosphere turbulent fluxes associated with atmospheric cyclones

An attempt was made to verify and further investigate a proposed relationship between the location of the maximum east-west sea surface temperature anomaly gradient (ΔSSTA) and the location of the maximum meridional component of the anomalous 700 mb geostrophic wind (VgA) in the North Pacific on a monthly and seasonal time scale. Previous empirical studies, mostly of a case study type, had suggested collocation of maximum values of these variables in the same time period, particularly during the cold seasons. Using 31 years of monthly sea surface temperature and 700 mb height data for the North Pacific, the two variables wore computed for each month and 3-month periods for each 10° longitude sector from 125°W to 155°E, and for each of three latitude bands (55–40°N, 40–25°N, 55–25°N). From these calculations, the spatial relationships of the two variables wore determined by counting frequencies of the collocation of maximum VgA and ΔSSTA for each month or season and latitude band, and by computing...

Anthony S. Broccoli

Papers

Associations between Sea Surface Temperature Gradient and Overlying Mid-Tropospheric Circulation in the North Pacific Region