•Whenever it snows in Britain we are taken by surprise

• I am surprised at you.

at/by/WITH/ABOUT
https://forum.wordreference.com/threads/i-was-surprised-at-by-with-the-news.525436/
https://www.englishforums.com/English/SurprisedSurprisedAboutSurprised/jvjnb/post.htm
https://forum.wordreference.com/threads/surprised-at-about-of-by.2252202/

По крайней мере до 2000 года было так:

https://books.google.com/ngrams/graph?content=I+was+surprised+by%2CI+was+surprised+at%2CI+was+surprised+with%2CI+was+surprised+above&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2CI was surprised by%3B%2Cc0%3B.t1%3B%2CI was surprised at%3B%2Cc0%3B.t1%3B%2CI was surprised with%3B%2Cc0%3B.t1%3B%2CI was surprised above%3B%2Cc0

about, not above
"I was" is irrelevant
But this doesn't change the results significantly

Sorry. Опечатка
А почему бы и нет, was как один из множества вариантов.
Подставил и I am

https://books.google.com/ngrams/graph?content=I+was+surprised+by%2CI+was+surprised+at%2CI+was+surprised+with%2CI+was+surprised+about%2CI+am+surprised+about&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2CI was surprised by%3B%2Cc0%3B.t1%3B%2CI was surprised at%3B%2Cc0%3B.t1%3B%2CI was surprised with%3B%2Cc0%3B.t1%3B%2CI was surprised about%3B%2Cc0%3B.t1%3B%2CI am surprised about%3B%2Cc0

Язык конечно меняется в связи с новой волной эммигрантов. Но до 2000 дела обстояли так в литературе

https://books.google.com/ngrams/graph?content=was+surprised+by%2Cwas+surprised+at%2Cwas+surprised+with%2Cis+surprised+about%2Cwas+surprised+about%2Cam+surprised+about&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cwas surprised by%3B%2Cc0%3B.t1%3B%2Cwas surprised at%3B%2Cc0%3B.t1%3B%2Cwas surprised with%3B%2Cc0%3B.t1%3B%2Cis surprised about%3B%2Cc0%3B.t1%3B%2Cwas surprised about%3B%2Cc0%3B.t1%3B%2Cam surprised about%3B%2Cc0

Конечно вариант, но, скорее всего, не имеющий отношения к вопросу.
e.g. surprised above expectations - это вовсе не "удивлен ожиданиями"
"I am" is irrelevant too
Также встречается "surprised on", но еще реже, и зависит от контекста.
"be surprised on this matter", но "was surprised on the first day"
https://books.google.com/ngrams/graph?content=surprised+by%2C+surprised+at%2C+surprised+with%2Csurprised+about%2C+surprised+on&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Csurprised%20by%3B%2Cc0%3B.t1%3B%2Csurprised%20at%3B%2Cc0%3B.t1%3B%2Csurprised%20with%3B%2Cc0%3B.t1%3B%2Csurprised%20about%3B%2Cc0%3B.t1%3B%2Csurprised%20on%3B%2Cc0

Изначально вопрос был BE surprised. И about встречается конечно, но не very common

surprised by or surprised at?
The preposition following surprised holds the key to two different meanings. When the phrase means “caught unawares,” it’s surprised by, whereas surprised at means “struck with amazement.” Compare:
The intruders were surprised by the security guard.
She was surprised at how quickly it had grown.
In some contexts either meaning might apply, and so surprised by could possibly be used in the second sentence. But surprised at could not be used in the first without changing its meaning.

(The Cambridge Guide to English Usage)

"be" тоже несущественно, т.к. предлог, очевидно, не зависит ни от лица, ни от времени. Алекс, я не понимаю, что вы хотите сказать

Так и я не пойму что Вы хотели сказать🙂. Вы вроде говорили что I am, is не подходит к вопросу... Что то про About, хоть оно исчезающе мало встречается...

"irrelevant" в первую очередь означает "не относящийся к делу", "несущественный" (что бы ни говорил Lingvo наперекор др. словарям)
В ngram надо сравнивать surprised with/by/at/... - без всяких I/you/he/she/... и без be/am/is/are - именно это я хотел сказать и добавил, что на результат это влияет мало. "Еще реже" я говорил про "on"

Ну раз мало, то и не о чем спорить 👍😉

Спасибо большое)