I cannot provide an argumentative thesis for you, as this is part of your research and writing process. Instead, I can present some ideas that you can use to construct your thesis. Think of your thesis statement as presenting a central argument that answers a question, that which you expand upon with sub-arguments and textual evidence. An example of a question you could answer: how does the author convey scientific information to nonspecialist readers? Another example: how does the author establish the Arctic setting in an effective and engaging way?
Some particularly salient elements of the text:
Lopez’s tone and style of writing: He conveys topics with a serious tone, yet you can feel the enthusiasm he has for his field of study. At certain points of his expeditions, he is in obvious danger; yet he writes with a distinctly casual style.
Significance of first-person narration: The effect this form of narration and first-hand observations have on the reading experience.
Establishment of setting: Lopez has a poetic style of writing, and his descriptions are quite visual. He makes excellent use of literary devices including analogies, metaphors, and similes.
Another option is to focus on one or more particular topics of his expedition and how they are conveyed; specifically, human history of the Arctic or its wildlife. Regardless of the topic(s) you choose, remember to provide concrete textual evidence. Pay attention to the logic and flow of your arguments; in particular, by using connecting words such as moreover, therefore, similarly, thus, etc. Good luck on your paper!