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Featured researches published by Kira T. Lawrence.


Science | 2009

Greatly Expanded Tropical Warm Pool and Weakened Hadley Circulation in the Early Pliocene

Chris M. Brierley; Alexey V. Fedorov; Zhonghui Liu; Timothy D. Herbert; Kira T. Lawrence; Jonathan P. LaRiviere

The Pliocene warm interval has been difficult to explain. We reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago, during the early Pliocene. Our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced, implying a vast poleward expansion of the ocean tropical warm pool. Corroborating evidence indicates that the Pacific temperature contrast between the equator and 32°N has evolved from ∼2°C 4 million years ago to ∼8°C today. The meridional warm pool expansion evidently had enormous impacts on the Pliocene climate, including a slowdown of the atmospheric Hadley circulation and El Niño–like conditions in the equatorial region. Ultimately, sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake (such as enhanced ocean vertical mixing).


Nature | 2013

Patterns and mechanisms of early Pliocene warmth

Alexey V. Fedorov; Chris M. Brierley; Kira T. Lawrence; Zhonghui Liu; P. S. Dekens; Ana Christina Ravelo

About five to four million years ago, in the early Pliocene epoch, Earth had a warm, temperate climate. The gradual cooling that followed led to the establishment of modern temperature patterns, possibly in response to a decrease in atmospheric CO2 concentration, of the order of 100 parts per million, towards preindustrial values. Here we synthesize the available geochemical proxy records of sea surface temperature and show that, compared with that of today, the early Pliocene climate had substantially lower meridional and zonal temperature gradients but similar maximum ocean temperatures. Using an Earth system model, we show that none of the mechanisms currently proposed to explain Pliocene warmth can simultaneously reproduce all three crucial features. We suggest that a combination of several dynamical feedbacks underestimated in the models at present, such as those related to ocean mixing and cloud albedo, may have been responsible for these climate conditions.


Science | 2010

Tropical Ocean Temperatures Over the Past 3.5 Million Years

Timothy D. Herbert; Laura Cleaveland Peterson; Kira T. Lawrence; Zhonghui Liu

Birth of the Cool Over the past 4 million years or so, tropical sea surface temperatures have experienced a cooling trend (see the Perspective by Philander). Herbert et al. (p. 1530) analyzed sea surface temperature records of the past 3.5 million years from low-latitude sites spanning the worlds major ocean basins in order to determine the timing and magnitude of the cooling that has accompanied the intensification of Northern Hemisphere ice ages since the Pliocene. Martínez-Garcia et al. (p. 1550) found that the enigmatic eastern equatorial Pacific cold tongue, a feature one might not expect to find in such a warm region receiving so much sunlight, first appeared between 1.8 and 1.2 million years ago. Its appearance was probably in response to a general shrinking of the tropical warm water pool caused by general climate cooling driven by changes in Earths orbit. Tropical sea surface temperatures were controlled more by atmospheric connections to glaciation cycles than by ocean circulation. Determining the timing and amplitude of tropical sea surface temperature (SST) change is an important part of solving the puzzle of the Plio-Pleistocene ice ages. Alkenone-based tropical SST records from the major ocean basins show coherent glacial-interglacial temperature changes of 1° to 3°C that align with (but slightly lead) global changes in ice volume and deep ocean temperature over the past 3.5 million years. Tropical temperatures became tightly coupled with benthic δ18O and orbital forcing after 2.7 million years. We interpret the similarity of tropical SST changes, in dynamically dissimilar regions, to reflect “top-down” forcing through the atmosphere. The inception of a strong carbon dioxide–greenhouse gas feedback and amplification of orbital forcing at ~2.7 million years ago connected the fate of Northern Hemisphere ice sheets with global ocean temperatures since that time.


Science | 2014

Antarctic role in Northern Hemisphere glaciation

Stella Woodard; Yair Rosenthal; Kenneth G. Miller; James D. Wright; Beverly K. Chiu; Kira T. Lawrence

Earth’s climate underwent a major transition from the warmth of the late Pliocene, when global surface temperatures were ~2° to 3°C higher than today, to extensive Northern Hemisphere glaciation (NHG) ~2.73 million years ago (Ma). We show that North Pacific deep waters were substantially colder (4°C) and probably fresher than the North Atlantic Deep Water before the intensification of NHG. At ~2.73 Ma, the Atlantic-Pacific temperature gradient was reduced to <1°C, suggesting the initiation of stronger heat transfer from the North Atlantic to the deep Pacific. We posit that increased glaciation of Antarctica, deduced from the 21 ± 10–meter sea-level fall from 3.15 to 2.75 Ma, and the development of a strong polar halocline fundamentally altered deep ocean circulation, which enhanced interhemispheric heat and salt transport, thereby contributing to NHG. Ice sheet growth in Antarctica preceded the intensification of Northern Hemispheric glaciation in the Pliocene. [Also see Perspective by McKay] Leading a wintry march from a distance When the Antarctic ice sheet began to expand around 3 million years ago, it caused changes in deep ocean circulation, hastening the pace of glaciation in the Northern Hemisphere. Woodard et al. analyzed marine sediments from the northwest Pacific Ocean. A substantial fraction of the sea level fall actually occurred before the Northern Hemispheric ice sheets began to grow rapidly, probably because of continental ice growth in Antarctica. Thus, Antarctic glaciers appear to be more dynamic than anticipated, which has implications for the stability of the Antarctic ice sheet in a warming world. Science, this issue p. 847


Paleoceanography | 2009

Change point method for detecting regime shifts in paleoclimatic time series: Application to δ18O time series of the Plio-Pleistocene

Eric Ruggieri; T. D. Herbert; Kira T. Lawrence; Charles E. Lawrence

[1] Although different paleoenvironmental time series resolve past climatic change at different time scales, nearly all share one characteristic: they are nonstationary over the length of the record sampled. We describe a recursive dynamic programming change point algorithm that is well suited to identify shifts in the Earth system’s variability, as it represents a nonstationary time series as a series of regimes, each of which is homogeneous. The algorithm fits the data by minimizing squared errors not only over the parameters of the models for each subsequence but also over an arbitrary number of boundary points without restrictions on the lengths of regimes. The versatility of the algorithm is illustrated by an application to 5 Ma of Plio-Pleisotcene d 18 O variations. We seek to identify either the single dominant ‘‘Milankovitch’’ frequency or linear combinations of frequencies and consistently identify changes � 780 ka and � 2.7 Ma, among others, in each analysis done. Our applications also provide support to the recent hypothesis that obliquity-based Milankovitch terms can account for the circa 100 ka cycle that empirically dominates the most recent 1 million years.


Paleoceanography | 2017

Past sea surface temperatures as measured by different proxies—A cautionary tale from the late Pliocene

Kira T. Lawrence; S. C. Woodard

The paleoclimate community uses a variety of different proxies to reconstruct past sea surface temperatures. Estimates from different paleothermometers are often used interchangeably despite a scarcity of studies exploring the validity of this practice. Here, we provide an orbital resolution case study from the Pliocene using Mg/Ca and alkenone paleothermometry that reinforces results from previous studies showing consistent estimates for some climate parameters and inconsistent results for others. We argue that the paleoclimate community should undertake an effort to more systematically evaluate if, when, and where climate estimates from different paleothermometers can be used interchangeably.


Science | 2006

Evolution of the Eastern Tropical Pacific Through Plio-Pleistocene Glaciation

Kira T. Lawrence; Zhonghui Liu; Timothy D. Herbert


Paleoceanography | 2009

High-amplitude variations in North Atlantic sea surface temperature during the early Pliocene warm period

Kira T. Lawrence; Timothy D. Herbert; Catherine M. Brown; Maureen E. Raymo; Alan M. Haywood


Paleoceanography | 2010

Last Glacial Maximum to Holocene sea surface conditions at Umnak Plateau, Bering Sea, as inferred from diatom, alkenone, and stable isotope records

Beth E. Caissie; Julie Brigham-Grette; Kira T. Lawrence; Timothy D. Herbert; Mea S. Cook


Nature Geoscience | 2016

Late Miocene global cooling and the rise of modern ecosystems

Timothy D. Herbert; Kira T. Lawrence; Alexandrina Tzanova; Laura Cleaveland Peterson; Rocio P Caballero-Gill; Christopher S Kelly

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Zhonghui Liu

University of Hong Kong

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Isabel Cacho

University of Barcelona

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