Daianne defended her MSc Thesis!

A group photo at the end of her defense! Daianne (top left) with her advisor, Dr. Yige Zhang (second from the left; top row) have delivered intriging findings of Clarkia Lake Deposit with TAMU Oceanography, alongside with her MSc thesis committee members: Dr. Ethan Grossman (second from the right; top row), Dr. Jason West (first from the left, second row), and Dr. Franco Marcantonio (second from the left; second row).

On March 11th, 2021, Daianne defended her thesis titled “Annually-resolved Sedimentation of the Middle Miocene Clarkia Lake Deposit (USA)”. It addressed the sedimentation history and age model of the world-renewed Clarkia Lake Deposit in Idaho. Her committee was chaired by Dr. Yige Zhang and formed by Dr. Ethan Grossman, Dr. Franco Marcantonio, and Dr. Jason West from Texas A&M University.

Her master thesis has been accepted as a peer-reviewed article in the journal Geology. In collaboration with researchers at Texas A&M University, Woods Hole Oceanographic Institution, and Bryant University, this research successfully places this deposit in the Middle Miocene Climate Optimum using radiometric methods. It also resolved the sedimentation resolution, establishing a millennium as total lake deposition. This article is in press; stay tuned for more detailed information about her results in the following weeks!

We are proud of you, Daianne! We could not wait to see your bright future.

Daianne won prestigious Outstanding Student Presentation Awards at the Fall AGU Meeting 2019

Daianne and her faculty advisor, Dr. Yige Zhang, proudly presented their awesome work with a wonderful scientific poster!

On the second week of December 2019, the George R. Moscone Convention Center, the largest convention center in San Francisco, CA, was bombarded by almost twenty-five thousand earth and space scientists. The American Geophysical Union (AGU) Fall Meeting is probably the largest annual earth and space sciences conference that gathers experts from all around the world to share their scientific discoveries that advances our understandings on Earth and Space sciences.

Daianne Höfig, a second-year MSc student from our research grounp, presented her work on the investigation of paleo-carbon dioxide during the Middle Miocene Climate Optimum (MMCO), ca. 15 million years ago (Ma). The high-resolution records of chemical variations were made possible regarding well-preserved valve-like lake deposits, where presumed annual layers can be identified based on light and dark bands of sediments. Preliminary results of her research show a positive correlation between the rates CO2 waxing and waning with future climatic models (e.g., Archer et al., 2009).

Each year, the top 2-5 percent of student presenters in each section are awarded an Outstanding Student Presentation Award (OSPA). Her presentation grabbed lots of attention form wider audiences and won the OSPA award in the section she participated in. We are so proud of Daianne! Congratulations!

1965: The first time in human history to live in a high CO2 world

Dr. Zhang has co-authored a study revealing that Earth’s carbon dioxide atmospheric concentrations averaged 250 parts per million for 2.5 million years. For refernece, today’s levels are about 410 parts per million.

On September 25, 2019, the research “Low CO2 levels of the entire Pleistocene Epoch” published in Nature Communications and has intrigued media and public audience by its findings.

Analyzing Paleogenic carbonates found in the ancient soil from the Loess Plateau, scientists reconstructed the Earth’s carbon dioxide levels. | Photo courtesy of Dr. Yige Zhang

Conventional “gold-standard” records of atmospheric carbon dioxide are commonly retrieved from ice cores. However, the ice-derived carbon dioxide records extend back only for the last 800,000 years. With Dr.Zhang’s co-authored study, soil carbonates from Leoss Plateau in central China recorded information that scientists can use for reconstructing Earth’s atmospheric carbon dioixide concentrations extending back since 2.5 million years ago (Ma). The study shows that the average level of carbon dioxide over the last 2.5 Ma was 230 parts per million (ppm).

“According to this research, from the first Homo erectus, which is currently dated to 2.1 to1.8 million years ago, until 1965, we have lived in a low-carbon dioxide environment — concentrations were less than 320 parts per million,” said Dr. Zhang, “We evolved in a low-carbon-dioxide environment, and how humans will evolve and be affected by today’s carbon-dioxide levels is yet to be seen.”

If you don’t want to miss what others are talking about, please check out articles in the media:

Nature communitcations: https://www.nature.com/articles/s41467-019-12357-5
Texas A&M Today: https://today.tamu.edu/2019/09/25/humankind-did-not-live-with-a-high-carbon-dioxide-atmosphere-until-1965/
KBTX-TV: https://www.kbtx.com/content/news/Doctor-Higher-carbon-dioxide-levels-could-lead-to-health-issues-561567141.html
Newsweek: https://www.newsweek.com/humans-co2-concentrations-earth-atmosphere-today-experiment-ourselves-1461495
ZME Science:

September 25, 2019 – Dr.Zhang gave some insights about the newly-published study on television at KBTX-TV: https://www.kbtx.com/templates/2015_Sub_Video_Share?contentObj=561567141

Spring Break fieldwork

Before sampling, it is important to photograph the exact location from where the sample is coming for precise stratigraphic control.
Dr. Hong Yang at left, Daianne Höfig at right.

During the Spring Break, one of our lab-group members, Daianne Höfig, took part in fieldwork in north Idaho! She is a first-year MSc student at Texas A&M University, under the supervision of Dr. Yige Zhang, and studies carbon dioxide variations during the middle Miocene using biomarkers.

To achieve this goal, she sampled fossil leaves of different angiosperm species that lived 15 million years ago that were preserved in extraordinary conditions in Clarkia Lake deposit. This deposit is located in a property of the Kienbaum family, in the small town of Clarkia, who allows scientific research in their area since the 1970s.

Such an intriguing project is a joint collaboration with Bryant University: Dr. Hong Yang belongs to the second generation of researchers to study this deposit. While the Bryant team if focused on the complex paleontological aspects of this endeavor, the Texas A&M team aims to understand the chemical signatures related to the seasonal sedimentation cycles and their relationship with the paleo-carbon dioxide levels.

Fossil leaf from the Clarkia Lake deposit! Can you believe it is about 15 million years old? It still preserves the fall colors!

Export Depth of the TEX86 Signal

Published on Paleoceanography and Paleoclimatology, doi:10.1029/2018PA003337.


Fig. 3


TEX86 is widely used for evaluating ancient ocean temperatures. However, the debate on the export depth of the TEX86 signal in the water column has not been settled. Consequently, TEX86 has been interpreted as/calibrated to surface, shallow subsurface or deep subsurface temperatures.  Here we examine the published core-top TEX86 data between 30°N to 30°S where the ocean temperatures at the surface show a clear latitudinal gradient, but not at the deep subsurface. The meridional distribution of the TEX86 data exhibits an inverted “U-shape” with the peak near the equator, which closely resembles the surface and shallow subsurface ocean temperature profiles. And the strongest correlation was identified between TEX86 and SSTs (sea surface temperatures). These results suggest that on the global scale, TEX86 is a proxy for temperatures of the epipelagic ocean less than 200 m deep.


A long history of equatorial deep-water upwelling in the Pacific Ocean

Published on Earth Planet. Sci. Lett, 2017, 467, 1-9. 


Graphical Abstract_Small


Cold, nutrient- and CO2-rich waters upwelling in the eastern equatorial Pacific (EEP) give rise to the Pacific cold tongue. Quasi-periodic subsidence of the thermocline and attenuation in wind strength expressed by El Niño conditions decrease upwelling rates, increase surface-water temperatures in the EEP, and lead to changes in regional climates both near and far from the equatorial Pacific. EEP surface waters have elevated CO2 concentrations during neutral (upwelling) or La Niña (strong upwelling) conditions. In contrast, approximate air-sea CO2 equilibrium characterizes El Niño events. One hypothesis proposes that changes in physical oceanography led to the establishment of a deep tropical thermocline and expanded mixed-layer prior to 3 million years ago. These effects are argued to have substantially reduced deep-water upwelling rates in the EEP and promoted a “permanent El Niño-like” climate state. For this study, we test this supposition by reconstructing EEP “excess CO2” and upwelling history for the past 6.5 million years using the alkenone-pCO2 methodology. Contrary to previous assertions, our results indicate that average temporal conditions in the EEP over the past ~6.5 million years were characterized by substantial CO2 disequilibrium and high nutrient delivery to surface waters — characteristics that imply strong upwelling of deep waters. Upwelling appears most vigorous between ~6.5 to 4.5 million years ago coinciding with high accumulation rates of biogenic material during the late Miocene – early Pliocene “biogenic bloom”.


In memoriam: Mark Pagani

photo: Mark, Ping, Yabo and Yige, October 2014

In memoriam: Mark Pagani, my advisor and my friend

November 16th, 2016 (Guam Time). I was about to write an email to Mark. It’s been a few days since I last wrote to him. He was too weak to respond to emails, but one of his best friends, Eric, who also lives in New Haven said Mark read my previous emails and was pleased. So since I board the research vessel JOIDES Resolution as a shipboard scientist, I started to write to him by emailing or texting (when we had cell phone reception). Today I was going to write “when you are well again, don’t ever sign up as an organic geochemist to sail on the JR. The organic geochemist’s job is mostly sediment crushing and weighing, but we never get the exciting findings as the paleontologists do”. Then, I received an email from Mark’s student Hui, and James a couple minutes later, saying “Mark passed away this afternoon”.

I pretended that it was ok. I pretended that we knew it’s going to happen. I tried to stay calm and wrote to Eric asking if there’s anything I can do for Mark and his family. Very quickly he replied with two words “Be famous”. The moment I saw this I burst into tears. It’s him! It’s Mark! It must be him! His voice was in my head again: “you will be famous, Yige”. For many times, we joked about that I would become a famous guy in China, so when he visits the country, he would be welcomed by red carpets and referred to as “the old friend of the Chinese people” – the highest recognition that only the revolutionary leaders such as Castro were called. We were joking but we were also serious. I know him as an advisor wants to see every one of his students to be successful. I know myself as a student wants to make my advisor proud. I felt really bad since I realized I would never have the chance to pay him back.

Mark is known to be blunt, and abrasive in some cases. I told him he shouldn’t show up at the graduate student recruiting weekend because he often scares people away. I teased him by saying that after I interviewed at Yale, I thought he’s a horrible person and he should totally thank the other professors who made me want to stay. As I often say, it doesn’t matter where you come from, anyone who just starts to deal with Mark would have a “culture shock”. Yes, I believe he had his own culture that might come from another planet. But he could be very sweet, although he tried really hard not to show that. One day I dealt with some really really rude people and I was very upset. I closed the door of my office and barricaded myself for hours. He knocked open and asked me what was going on. Then, he invited me to come to his office, treated me with the best from his secret stash of liquor (not sure if any university codes were violated), and explained the neighborhood he grew up where “you leave a donut outside, people would take it”, and how I should deal with nasty people and big bullies. We spent the entire afternoon together, just drinking and chatting. Mark’s friend Pam said he is a “pussy cat”. Nobody believed her, but I tend to agree with that.

I met Mark Pagani in December 2008, San Francisco, CA. He was wearing glasses with a black frame, and a leather jacket. I saw Mark Pagani the very last time in April 2016, Cambridge, MA. He was wearing glasses with a black frame, and a leather jacket. It seems nothing has changed. I know that at this very moment, he must have the same appearance in the other world. He might be reading “New York Times” on his Macintosh, or painting in a studio, or building a shed – I’m not sure. But I feel lucky that I met him, had him as my advisor and my friend for the last eight years. 再见,老马。再见,我的朋友。