Interpreting the sedimentary record I Distributions represent processes Physical (temperature, salinity, density) Chemical (nutrients, recycled and scavenged elements) II Identify faithful recorders (proxies) Sediment chemistry, microfossil type, shell chemistry III Interpretation Reconstruct distributions Infer paleo-processes IV Ground-truth / calibration: Modern oceanographic processes Modern sea-floor sediments (core tops)

May reflect more than one process, more than one path. Distributions May reflect more than one process, more than one path. Recorders What do the proxies record? Where? When? (property) (depth habitat) (seasonality) Reconstruction Spatial distribution of paleo data (point, transect, map, 3D) Chronology -- Time slice -- Time series. Interpretation Is the present the key to the past? Distribution ≠ rate

Bio-limiting, bio-intermediate, and bio-unlimited elements

Conservative Invariant with depth. Pacific = Atlantic Recycled Increase downward. Pacific > Atlantic Scavenged Decrease downward. Pacific < Atlantic

Sea-surface temperature Examples: Sea-surface temperature Calcium-carbonate accumulation Deep-ocean circulation

Sea-surface temperature (SST)

CLIMAP SST Reconstruction of past sea-surface temperatures using statistical (multi- variate) approach to analyzing microfossil assemblages. In this case, planktonic foraminifera shells.

Faunal assemblages Microfossils reflect the predominant planktonic species at a given location. A handful dominate in the tropics.

Faunal assemblages A second assemblage occurs primarily in the subtropics.

Faunal assemblages Another assemblage occupies the subpolar regions.

Faunal assemblages A single species of foraminifera is predominant in polar regions.

Faunal assemblages Observations can be combined to draw inferences about past environments. CLIMAP used a multi-variate statistical approach.

Transfer functions The assemblage data, combined as factors, provide a regression with variables such as SST. Predictions based on these relationships can be tested against other datasets to evaluate the success of the method.

CLIMAP SST Strong cooling at high latitudes and little change in the tropics. Modern LGM

CaCO3 accumulation and evidence for lysocline changes Cores from eastern equatorial Pacific display variations in CaCO3, suggesting repeated shoaling and deepening of dissolution horizon. Core depths

Did the CaCO3 saturation horizon (lysocline) shift at the LGM?

Higher at LGM in the Pacific. Lower at LGM in other oceans. CaCO3 content Higher at LGM in the Pacific. Lower at LGM in other oceans. ATL IND SOU PAC

CaCO3 flux Regional estimates of CaCO3 mass accumulation rates.

CaCO3 flux Global sum = little change. Holocene slightly higher. Does flux = lysocline?

Ocean circulation Evident in many physical properties. Proxies utilize influence of biology. Biological pump Vertical flux of organic matter and hard parts from surface to the deep sea. Superimposed on deep ocean circulation.

Evident in salinity and many other properties… The meridional overturning circulation (MOC) produces North Atlantic Deep Water (NADW). NADW GEOSECS Evident in salinity and many other properties…

Biological pump Surface productivity utilizes nutrients and carbon. Gravity moves them to the deep-sea, and respiration returns them to the seawater.

Vertical rain of carbon is highest near the surface Carbon fluxes Vertical rain of carbon is highest near the surface and declines with depth, Indicating remineralization within the water column. (Data from N. Pacific sediment traps) Martin et al. (1987)

Productivity Biological activity results in systematic changes in concentration and isotopic ratio of bio-limiting and bio-intermediate elements.

Nutrients as tracers Nutrients at depth are swept “downstream” by the global ocean circulation.

SST, density, and nutrients High latitude surface waters in the north are nutrient-depleted. waters in the south are nutrient-rich. Deep-waters formed at the two poles display strong chemical contrast.

Surface water O2 Surface waters (over) saturated due to bubble injection and photosynthesis.

Deep water O2 Deep waters become depleted due to respiration along the circulation pathway.

Deep water O2 Apparent oxygen utilization reveals the pattern of deep ocean circulation.

Carbon isotopes Photosynthetic fractionation of organic carbon leaves seawater enriched in heavier carbon-13. The resulting Isotopic ratio in seawater is then incorporated in CaCO3, providing a nutrient-tracer.

Evident in salinity and many other properties… The meridional overturning circulation (MOC) produces North Atlantic Deep Water (NADW). NADW GEOSECS Evident in salinity and many other properties…

Also evident in carbon isotopes (d13C). The meridional overturning circulation (MOC) produces North Atlantic Deep Water (NADW). NADW Kroopnick (1985) Also evident in carbon isotopes (d13C).

LGM meridional section, western basin Paleocean circulation The configuration was different, but not the rate of circulation? Curry and Oppo (2005)